diff --git a/src/main/java/io/reactivex/Completable.java b/src/main/java/io/reactivex/Completable.java
index 0453b45462..372bb36c7c 100644
--- a/src/main/java/io/reactivex/Completable.java
+++ b/src/main/java/io/reactivex/Completable.java
@@ -929,6 +929,7 @@ public final void blockingAwait() {
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     public final boolean blockingAwait(long timeout, TimeUnit unit) {
+        ObjectHelper.requireNonNull(unit, "unit is null");
         BlockingMultiObserver<Void> observer = new BlockingMultiObserver<Void>();
         subscribe(observer);
         return observer.blockingAwait(timeout, unit);
diff --git a/src/main/java/io/reactivex/Flowable.java b/src/main/java/io/reactivex/Flowable.java
index 743c0ef419..237eac6243 100644
--- a/src/main/java/io/reactivex/Flowable.java
+++ b/src/main/java/io/reactivex/Flowable.java
@@ -1229,6 +1229,8 @@ public static <T> Flowable<T> concat(Publisher<? extends Publisher<? extends T>>
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     public static <T> Flowable<T> concat(Publisher<? extends T> source1, Publisher<? extends T> source2) {
+        ObjectHelper.requireNonNull(source1, "source1 is null");
+        ObjectHelper.requireNonNull(source2, "source2 is null");
         return concatArray(source1, source2);
     }
 
@@ -1265,6 +1267,9 @@ public static <T> Flowable<T> concat(Publisher<? extends T> source1, Publisher<?
     public static <T> Flowable<T> concat(
             Publisher<? extends T> source1, Publisher<? extends T> source2,
             Publisher<? extends T> source3) {
+        ObjectHelper.requireNonNull(source1, "source1 is null");
+        ObjectHelper.requireNonNull(source2, "source2 is null");
+        ObjectHelper.requireNonNull(source3, "source3 is null");
         return concatArray(source1, source2, source3);
     }
 
@@ -1303,6 +1308,10 @@ public static <T> Flowable<T> concat(
     public static <T> Flowable<T> concat(
             Publisher<? extends T> source1, Publisher<? extends T> source2,
             Publisher<? extends T> source3, Publisher<? extends T> source4) {
+        ObjectHelper.requireNonNull(source1, "source1 is null");
+        ObjectHelper.requireNonNull(source2, "source2 is null");
+        ObjectHelper.requireNonNull(source3, "source3 is null");
+        ObjectHelper.requireNonNull(source4, "source4 is null");
         return concatArray(source1, source2, source3, source4);
     }
 
@@ -1426,6 +1435,9 @@ public static <T> Flowable<T> concatArrayEager(Publisher<? extends T>... sources
     @SchedulerSupport(SchedulerSupport.NONE)
     @SuppressWarnings({ "rawtypes", "unchecked" })
     public static <T> Flowable<T> concatArrayEager(int maxConcurrency, int prefetch, Publisher<? extends T>... sources) {
+        ObjectHelper.requireNonNull(sources, "sources is null");
+        ObjectHelper.verifyPositive(maxConcurrency, "maxConcurrency");
+        ObjectHelper.verifyPositive(prefetch, "prefetch");
         return RxJavaPlugins.onAssembly(new FlowableConcatMapEager(new FlowableFromArray(sources), Functions.identity(), maxConcurrency, prefetch, ErrorMode.IMMEDIATE));
     }
 
@@ -1557,6 +1569,9 @@ public static <T> Flowable<T> concatEager(Publisher<? extends Publisher<? extend
     @SchedulerSupport(SchedulerSupport.NONE)
     @SuppressWarnings({ "rawtypes", "unchecked" })
     public static <T> Flowable<T> concatEager(Publisher<? extends Publisher<? extends T>> sources, int maxConcurrency, int prefetch) {
+        ObjectHelper.requireNonNull(sources, "sources is null");
+        ObjectHelper.verifyPositive(maxConcurrency, "maxConcurrency");
+        ObjectHelper.verifyPositive(prefetch, "prefetch");
         return RxJavaPlugins.onAssembly(new FlowableConcatMapEagerPublisher(sources, Functions.identity(), maxConcurrency, prefetch, ErrorMode.IMMEDIATE));
     }
 
@@ -1613,6 +1628,9 @@ public static <T> Flowable<T> concatEager(Iterable<? extends Publisher<? extends
     @SchedulerSupport(SchedulerSupport.NONE)
     @SuppressWarnings({ "rawtypes", "unchecked" })
     public static <T> Flowable<T> concatEager(Iterable<? extends Publisher<? extends T>> sources, int maxConcurrency, int prefetch) {
+        ObjectHelper.requireNonNull(sources, "sources is null");
+        ObjectHelper.verifyPositive(maxConcurrency, "maxConcurrency");
+        ObjectHelper.verifyPositive(prefetch, "prefetch");
         return RxJavaPlugins.onAssembly(new FlowableConcatMapEager(new FlowableFromIterable(sources), Functions.identity(), maxConcurrency, prefetch, ErrorMode.IMMEDIATE));
     }
 
@@ -6219,6 +6237,7 @@ public final <B> Flowable<List<T>> buffer(Publisher<B> boundaryIndicator) {
     @BackpressureSupport(BackpressureKind.ERROR)
     @SchedulerSupport(SchedulerSupport.NONE)
     public final <B> Flowable<List<T>> buffer(Publisher<B> boundaryIndicator, final int initialCapacity) {
+        ObjectHelper.verifyPositive(initialCapacity, "initialCapacity");
         return buffer(boundaryIndicator, Functions.<T>createArrayList(initialCapacity));
     }
 
@@ -6640,6 +6659,7 @@ public final <R> Flowable<R> concatMap(Function<? super T, ? extends Publisher<?
     @SchedulerSupport(SchedulerSupport.NONE)
     public final <R> Flowable<R> concatMap(Function<? super T, ? extends Publisher<? extends R>> mapper, int prefetch) {
         ObjectHelper.requireNonNull(mapper, "mapper is null");
+        ObjectHelper.verifyPositive(prefetch, "prefetch");
         if (this instanceof ScalarCallable) {
             @SuppressWarnings("unchecked")
             T v = ((ScalarCallable<T>)this).call();
@@ -6648,7 +6668,6 @@ public final <R> Flowable<R> concatMap(Function<? super T, ? extends Publisher<?
             }
             return FlowableScalarXMap.scalarXMap(v, mapper);
         }
-        ObjectHelper.verifyPositive(prefetch, "prefetch");
         return RxJavaPlugins.onAssembly(new FlowableConcatMap<T, R>(this, mapper, prefetch, ErrorMode.IMMEDIATE));
     }
 
@@ -6712,6 +6731,7 @@ public final <R> Flowable<R> concatMapDelayError(Function<? super T, ? extends P
     public final <R> Flowable<R> concatMapDelayError(Function<? super T, ? extends Publisher<? extends R>> mapper,
             int prefetch, boolean tillTheEnd) {
         ObjectHelper.requireNonNull(mapper, "mapper is null");
+        ObjectHelper.verifyPositive(prefetch, "prefetch");
         if (this instanceof ScalarCallable) {
             @SuppressWarnings("unchecked")
             T v = ((ScalarCallable<T>)this).call();
@@ -6720,7 +6740,6 @@ public final <R> Flowable<R> concatMapDelayError(Function<? super T, ? extends P
             }
             return FlowableScalarXMap.scalarXMap(v, mapper);
         }
-        ObjectHelper.verifyPositive(prefetch, "prefetch");
         return RxJavaPlugins.onAssembly(new FlowableConcatMap<T, R>(this, mapper, prefetch, tillTheEnd ? ErrorMode.END : ErrorMode.BOUNDARY));
     }
 
@@ -6779,6 +6798,7 @@ public final <R> Flowable<R> concatMapEager(Function<? super T, ? extends Publis
     @SchedulerSupport(SchedulerSupport.NONE)
     public final <R> Flowable<R> concatMapEager(Function<? super T, ? extends Publisher<? extends R>> mapper,
             int maxConcurrency, int prefetch) {
+        ObjectHelper.requireNonNull(mapper, "mapper is null");
         ObjectHelper.verifyPositive(maxConcurrency, "maxConcurrency");
         ObjectHelper.verifyPositive(prefetch, "prefetch");
         return RxJavaPlugins.onAssembly(new FlowableConcatMapEager<T, R>(this, mapper, maxConcurrency, prefetch, ErrorMode.IMMEDIATE));
@@ -6847,6 +6867,9 @@ public final <R> Flowable<R> concatMapEagerDelayError(Function<? super T, ? exte
     @SchedulerSupport(SchedulerSupport.NONE)
     public final <R> Flowable<R> concatMapEagerDelayError(Function<? super T, ? extends Publisher<? extends R>> mapper,
             int maxConcurrency, int prefetch, boolean tillTheEnd) {
+        ObjectHelper.requireNonNull(mapper, "mapper is null");
+        ObjectHelper.verifyPositive(maxConcurrency, "maxConcurrency");
+        ObjectHelper.verifyPositive(prefetch, "prefetch");
         return RxJavaPlugins.onAssembly(new FlowableConcatMapEager<T, R>(this, mapper, maxConcurrency, prefetch, tillTheEnd ? ErrorMode.END : ErrorMode.BOUNDARY));
     }
 
@@ -8390,6 +8413,8 @@ public final <R> Flowable<R> flatMap(Function<? super T, ? extends Publisher<? e
     public final <R> Flowable<R> flatMap(Function<? super T, ? extends Publisher<? extends R>> mapper,
             boolean delayErrors, int maxConcurrency, int bufferSize) {
         ObjectHelper.requireNonNull(mapper, "mapper is null");
+        ObjectHelper.verifyPositive(maxConcurrency, "maxConcurrency");
+        ObjectHelper.verifyPositive(bufferSize, "bufferSize");
         if (this instanceof ScalarCallable) {
             @SuppressWarnings("unchecked")
             T v = ((ScalarCallable<T>)this).call();
@@ -8398,8 +8423,6 @@ public final <R> Flowable<R> flatMap(Function<? super T, ? extends Publisher<? e
             }
             return FlowableScalarXMap.scalarXMap(v, mapper);
         }
-        ObjectHelper.verifyPositive(maxConcurrency, "maxConcurrency");
-        ObjectHelper.verifyPositive(bufferSize, "bufferSize");
         return RxJavaPlugins.onAssembly(new FlowableFlatMap<T, R>(this, mapper, delayErrors, maxConcurrency, bufferSize));
     }
 
@@ -8655,6 +8678,8 @@ public final <U, R> Flowable<R> flatMap(final Function<? super T, ? extends Publ
             final BiFunction<? super T, ? super U, ? extends R> combiner, boolean delayErrors, int maxConcurrency, int bufferSize) {
         ObjectHelper.requireNonNull(mapper, "mapper is null");
         ObjectHelper.requireNonNull(combiner, "combiner is null");
+        ObjectHelper.verifyPositive(maxConcurrency, "maxConcurrency");
+        ObjectHelper.verifyPositive(bufferSize, "bufferSize");
         return flatMap(FlowableInternalHelper.flatMapWithCombiner(mapper, combiner), delayErrors, maxConcurrency, bufferSize);
     }
 
@@ -9378,6 +9403,10 @@ public final <TRight, TLeftEnd, TRightEnd, R> Flowable<R> groupJoin(
             Function<? super T, ? extends Publisher<TLeftEnd>> leftEnd,
             Function<? super TRight, ? extends Publisher<TRightEnd>> rightEnd,
             BiFunction<? super T, ? super Flowable<TRight>, ? extends R> resultSelector) {
+        ObjectHelper.requireNonNull(other, "other is null");
+        ObjectHelper.requireNonNull(leftEnd, "leftEnd is null");
+        ObjectHelper.requireNonNull(rightEnd, "rightEnd is null");
+        ObjectHelper.requireNonNull(resultSelector, "resultSelector is null");
         return RxJavaPlugins.onAssembly(new FlowableGroupJoin<T, TRight, TLeftEnd, TRightEnd, R>(
                 this, other, leftEnd, rightEnd, resultSelector));
     }
@@ -9495,6 +9524,10 @@ public final <TRight, TLeftEnd, TRightEnd, R> Flowable<R> join(
             Function<? super T, ? extends Publisher<TLeftEnd>> leftEnd,
             Function<? super TRight, ? extends Publisher<TRightEnd>> rightEnd,
             BiFunction<? super T, ? super TRight, ? extends R> resultSelector) {
+        ObjectHelper.requireNonNull(other, "other is null");
+        ObjectHelper.requireNonNull(leftEnd, "leftEnd is null");
+        ObjectHelper.requireNonNull(rightEnd, "rightEnd is null");
+        ObjectHelper.requireNonNull(resultSelector, "resultSelector is null");
         return RxJavaPlugins.onAssembly(new FlowableJoin<T, TRight, TLeftEnd, TRightEnd, R>(
                 this, other, leftEnd, rightEnd, resultSelector));
     }
@@ -10003,6 +10036,7 @@ public final Flowable<T> onBackpressureBuffer(int capacity, boolean delayError,
     public final Flowable<T> onBackpressureBuffer(int capacity, boolean delayError, boolean unbounded,
             Action onOverflow) {
         ObjectHelper.requireNonNull(onOverflow, "onOverflow is null");
+        ObjectHelper.verifyPositive(capacity, "capacity");
         return RxJavaPlugins.onAssembly(new FlowableOnBackpressureBuffer<T>(this, capacity, unbounded, delayError, onOverflow));
     }
 
@@ -10986,6 +11020,7 @@ public final <R> Flowable<R> replay(Function<? super Flowable<T>, ? extends Publ
     @SchedulerSupport(SchedulerSupport.NONE)
     public final <R> Flowable<R> replay(Function<? super Flowable<T>, ? extends Publisher<R>> selector, final int bufferSize) {
         ObjectHelper.requireNonNull(selector, "selector is null");
+        ObjectHelper.verifyPositive(bufferSize, "bufferSize");
         return FlowableReplay.multicastSelector(FlowableInternalHelper.replayCallable(this, bufferSize), selector);
     }
 
@@ -11068,8 +11103,10 @@ public final <R> Flowable<R> replay(Function<? super Flowable<T>, ? extends Publ
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.CUSTOM)
     public final <R> Flowable<R> replay(Function<? super Flowable<T>, ? extends Publisher<R>> selector, final int bufferSize, final long time, final TimeUnit unit, final Scheduler scheduler) {
-        ObjectHelper.verifyPositive(bufferSize, "bufferSize");
         ObjectHelper.requireNonNull(selector, "selector is null");
+        ObjectHelper.requireNonNull(unit, "unit is null");
+        ObjectHelper.verifyPositive(bufferSize, "bufferSize");
+        ObjectHelper.requireNonNull(scheduler, "scheduler is null");
         return FlowableReplay.multicastSelector(
                 FlowableInternalHelper.replayCallable(this, bufferSize, time, unit, scheduler), selector);
     }
@@ -11107,6 +11144,9 @@ public final <R> Flowable<R> replay(Function<? super Flowable<T>, ? extends Publ
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.CUSTOM)
     public final <R> Flowable<R> replay(final Function<? super Flowable<T>, ? extends Publisher<R>> selector, final int bufferSize, final Scheduler scheduler) {
+        ObjectHelper.requireNonNull(selector, "selector is null");
+        ObjectHelper.requireNonNull(scheduler, "scheduler is null");
+        ObjectHelper.verifyPositive(bufferSize, "bufferSize");
         return FlowableReplay.multicastSelector(FlowableInternalHelper.replayCallable(this, bufferSize),
                 FlowableInternalHelper.replayFunction(selector, scheduler)
         );
@@ -11251,6 +11291,7 @@ public final <R> Flowable<R> replay(final Function<? super Flowable<T>, ? extend
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     public final ConnectableFlowable<T> replay(final int bufferSize) {
+        ObjectHelper.verifyPositive(bufferSize, "bufferSize");
         return FlowableReplay.create(this, bufferSize);
     }
 
@@ -11323,6 +11364,7 @@ public final ConnectableFlowable<T> replay(int bufferSize, long time, TimeUnit u
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.CUSTOM)
     public final ConnectableFlowable<T> replay(final int bufferSize, final long time, final TimeUnit unit, final Scheduler scheduler) {
+        ObjectHelper.verifyPositive(bufferSize, "bufferSize");
         ObjectHelper.requireNonNull(unit, "unit is null");
         ObjectHelper.requireNonNull(scheduler, "scheduler is null");
         ObjectHelper.verifyPositive(bufferSize, "bufferSize");
@@ -12591,6 +12633,7 @@ public final Flowable<T> sorted() {
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     public final Flowable<T> sorted(Comparator<? super T> sortFunction) {
+        ObjectHelper.requireNonNull(sortFunction, "sortFunction");
         return toList().toFlowable().map(Functions.listSorter(sortFunction)).flatMapIterable(Functions.<List<T>>identity());
     }
 
@@ -13226,6 +13269,7 @@ public final <R> Flowable<R> switchMapDelayError(Function<? super T, ? extends P
 
     <R> Flowable<R> switchMap0(Function<? super T, ? extends Publisher<? extends R>> mapper, int bufferSize, boolean delayError) {
         ObjectHelper.requireNonNull(mapper, "mapper is null");
+        ObjectHelper.verifyPositive(bufferSize, "bufferSize");
         if (this instanceof ScalarCallable) {
             @SuppressWarnings("unchecked")
             T v = ((ScalarCallable<T>)this).call();
@@ -13234,7 +13278,6 @@ <R> Flowable<R> switchMap0(Function<? super T, ? extends Publisher<? extends R>>
             }
             return FlowableScalarXMap.scalarXMap(v, mapper);
         }
-        ObjectHelper.verifyPositive(bufferSize, "bufferSize");
         return RxJavaPlugins.onAssembly(new FlowableSwitchMap<T, R>(this, mapper, bufferSize, delayError));
     }
 
@@ -14199,7 +14242,7 @@ public final Flowable<T> timeout(long timeout, TimeUnit timeUnit) {
     @CheckReturnValue
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.COMPUTATION)
-    public final Flowable<T> timeout(long timeout, TimeUnit timeUnit, Flowable<? extends T> other) {
+    public final Flowable<T> timeout(long timeout, TimeUnit timeUnit, Publisher<? extends T> other) {
         ObjectHelper.requireNonNull(other, "other is null");
         return timeout0(timeout, timeUnit, other, Schedulers.computation());
     }
@@ -14235,7 +14278,7 @@ public final Flowable<T> timeout(long timeout, TimeUnit timeUnit, Flowable<? ext
     @CheckReturnValue
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.CUSTOM)
-    public final Flowable<T> timeout(long timeout, TimeUnit timeUnit, Scheduler scheduler, Flowable<? extends T> other) {
+    public final Flowable<T> timeout(long timeout, TimeUnit timeUnit, Scheduler scheduler, Publisher<? extends T> other) {
         ObjectHelper.requireNonNull(other, "other is null");
         return timeout0(timeout, timeUnit, other, scheduler);
     }
@@ -14360,7 +14403,7 @@ public final <U, V> Flowable<T> timeout(
         return timeout0(firstTimeoutIndicator, itemTimeoutIndicator, other);
     }
 
-    private Flowable<T> timeout0(long timeout, TimeUnit timeUnit, Flowable<? extends T> other,
+    private Flowable<T> timeout0(long timeout, TimeUnit timeUnit, Publisher<? extends T> other,
             Scheduler scheduler) {
         ObjectHelper.requireNonNull(timeUnit, "timeUnit is null");
         ObjectHelper.requireNonNull(scheduler, "scheduler is null");
@@ -15572,6 +15615,7 @@ public final <B> Flowable<Flowable<T>> window(Publisher<B> boundaryIndicator) {
     @SchedulerSupport(SchedulerSupport.NONE)
     public final <B> Flowable<Flowable<T>> window(Publisher<B> boundaryIndicator, int bufferSize) {
         ObjectHelper.requireNonNull(boundaryIndicator, "boundaryIndicator is null");
+        ObjectHelper.verifyPositive(bufferSize, "bufferSize");
         return RxJavaPlugins.onAssembly(new FlowableWindowBoundary<T, B>(this, boundaryIndicator, bufferSize));
     }
 
@@ -15650,6 +15694,7 @@ public final <U, V> Flowable<Flowable<T>> window(
             Function<? super U, ? extends Publisher<V>> closingIndicator, int bufferSize) {
         ObjectHelper.requireNonNull(openingIndicator, "openingIndicator is null");
         ObjectHelper.requireNonNull(closingIndicator, "closingIndicator is null");
+        ObjectHelper.verifyPositive(bufferSize, "bufferSize");
         return RxJavaPlugins.onAssembly(new FlowableWindowBoundarySelector<T, U, V>(this, openingIndicator, closingIndicator, bufferSize));
     }
 
@@ -15719,6 +15764,7 @@ public final <B> Flowable<Flowable<T>> window(Callable<? extends Publisher<B>> b
     @SchedulerSupport(SchedulerSupport.NONE)
     public final <B> Flowable<Flowable<T>> window(Callable<? extends Publisher<B>> boundaryIndicatorSupplier, int bufferSize) {
         ObjectHelper.requireNonNull(boundaryIndicatorSupplier, "boundaryIndicatorSupplier is null");
+        ObjectHelper.verifyPositive(bufferSize, "bufferSize");
         return RxJavaPlugins.onAssembly(new FlowableWindowBoundarySupplier<T, B>(this, boundaryIndicatorSupplier, bufferSize));
     }
 
@@ -15792,6 +15838,8 @@ public final <U, R> Flowable<R> withLatestFrom(Publisher<? extends U> other,
     @SchedulerSupport(SchedulerSupport.NONE)
     public final <T1, T2, R> Flowable<R> withLatestFrom(Publisher<T1> source1, Publisher<T2> source2,
             Function3<? super T, ? super T1, ? super T2, R> combiner) {
+        ObjectHelper.requireNonNull(source1, "source1 is null");
+        ObjectHelper.requireNonNull(source2, "source2 is null");
         Function<Object[], R> f = Functions.toFunction(combiner);
         return withLatestFrom(new Publisher[] { source1, source2 }, f);
     }
@@ -15831,6 +15879,9 @@ public final <T1, T2, T3, R> Flowable<R> withLatestFrom(
             Publisher<T1> source1, Publisher<T2> source2,
             Publisher<T3> source3,
             Function4<? super T, ? super T1, ? super T2, ? super T3, R> combiner) {
+        ObjectHelper.requireNonNull(source1, "source1 is null");
+        ObjectHelper.requireNonNull(source2, "source2 is null");
+        ObjectHelper.requireNonNull(source3, "source3 is null");
         Function<Object[], R> f = Functions.toFunction(combiner);
         return withLatestFrom(new Publisher[] { source1, source2, source3 }, f);
     }
@@ -15872,6 +15923,10 @@ public final <T1, T2, T3, T4, R> Flowable<R> withLatestFrom(
             Publisher<T1> source1, Publisher<T2> source2,
             Publisher<T3> source3, Publisher<T4> source4,
             Function5<? super T, ? super T1, ? super T2, ? super T3, ? super T4, R> combiner) {
+        ObjectHelper.requireNonNull(source1, "source1 is null");
+        ObjectHelper.requireNonNull(source2, "source2 is null");
+        ObjectHelper.requireNonNull(source3, "source3 is null");
+        ObjectHelper.requireNonNull(source4, "source4 is null");
         Function<Object[], R> f = Functions.toFunction(combiner);
         return withLatestFrom(new Publisher[] { source1, source2, source3, source4 }, f);
     }
diff --git a/src/main/java/io/reactivex/Maybe.java b/src/main/java/io/reactivex/Maybe.java
index 06a1ede963..1065dc06f0 100644
--- a/src/main/java/io/reactivex/Maybe.java
+++ b/src/main/java/io/reactivex/Maybe.java
@@ -827,6 +827,8 @@ public static <T> Flowable<T> merge(Publisher<? extends MaybeSource<? extends T>
     @SchedulerSupport(SchedulerSupport.NONE)
     @SuppressWarnings({ "unchecked", "rawtypes" })
     public static <T> Flowable<T> merge(Publisher<? extends MaybeSource<? extends T>> sources, int maxConcurrency) {
+        ObjectHelper.requireNonNull(sources, "source is null");
+        ObjectHelper.verifyPositive(maxConcurrency, "maxConcurrency");
         return RxJavaPlugins.onAssembly(new FlowableFlatMapPublisher(sources, MaybeToPublisher.instance(), false, maxConcurrency, Flowable.bufferSize()));
     }
 
@@ -852,6 +854,7 @@ public static <T> Flowable<T> merge(Publisher<? extends MaybeSource<? extends T>
     @SchedulerSupport(SchedulerSupport.NONE)
     @SuppressWarnings({ "unchecked", "rawtypes" })
     public static <T> Maybe<T> merge(MaybeSource<? extends MaybeSource<? extends T>> source) {
+        ObjectHelper.requireNonNull(source, "source is null");
         return RxJavaPlugins.onAssembly(new MaybeFlatten(source, Functions.identity()));
     }
 
@@ -1028,6 +1031,9 @@ public static <T> Flowable<T> mergeArray(MaybeSource<? extends T>... sources) {
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     public static <T> Flowable<T> mergeArrayDelayError(MaybeSource<? extends T>... sources) {
+        if (sources.length == 0) {
+            return Flowable.empty();
+        }
         return Flowable.fromArray(sources).flatMap((Function)MaybeToPublisher.instance(), true, sources.length);
     }
 
@@ -1309,6 +1315,9 @@ public static <T> Single<Boolean> sequenceEqual(MaybeSource<? extends T> source1
     @SchedulerSupport(SchedulerSupport.NONE)
     public static <T> Single<Boolean> sequenceEqual(MaybeSource<? extends T> source1, MaybeSource<? extends T> source2,
             BiPredicate<? super T, ? super T> isEqual) {
+        ObjectHelper.requireNonNull(source1, "source1 is null");
+        ObjectHelper.requireNonNull(source2, "source2 is null");
+        ObjectHelper.requireNonNull(isEqual, "isEqual is null");
         return RxJavaPlugins.onAssembly(new MaybeEqualSingle<T>(source1, source2, isEqual));
     }
 
@@ -2281,6 +2290,7 @@ public final Maybe<T> delay(long delay, TimeUnit unit, Scheduler scheduler) {
     @SchedulerSupport(SchedulerSupport.NONE)
     @BackpressureSupport(BackpressureKind.UNBOUNDED_IN)
     public final <U, V> Maybe<T> delay(Publisher<U> delayIndicator) {
+        ObjectHelper.requireNonNull(delayIndicator, "delayIndicator is null");
         return RxJavaPlugins.onAssembly(new MaybeDelayOtherPublisher<T, U>(this, delayIndicator));
     }
 
@@ -2677,6 +2687,8 @@ public final <R> Maybe<R> flatMap(
     @SchedulerSupport(SchedulerSupport.NONE)
     public final <U, R> Maybe<R> flatMap(Function<? super T, ? extends MaybeSource<? extends U>> mapper,
             BiFunction<? super T, ? super U, ? extends R> resultSelector) {
+        ObjectHelper.requireNonNull(mapper, "mapper is null");
+        ObjectHelper.requireNonNull(resultSelector, "resultSelector is null");
         return RxJavaPlugins.onAssembly(new MaybeFlatMapBiSelector<T, U, R>(this, mapper, resultSelector));
     }
 
@@ -2704,6 +2716,7 @@ public final <U, R> Maybe<R> flatMap(Function<? super T, ? extends MaybeSource<?
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     public final <U> Flowable<U> flattenAsFlowable(final Function<? super T, ? extends Iterable<? extends U>> mapper) {
+        ObjectHelper.requireNonNull(mapper, "mapper is null");
         return RxJavaPlugins.onAssembly(new MaybeFlatMapIterableFlowable<T, U>(this, mapper));
     }
 
@@ -2727,6 +2740,7 @@ public final <U> Flowable<U> flattenAsFlowable(final Function<? super T, ? exten
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     public final <U> Observable<U> flattenAsObservable(final Function<? super T, ? extends Iterable<? extends U>> mapper) {
+        ObjectHelper.requireNonNull(mapper, "mapper is null");
         return RxJavaPlugins.onAssembly(new MaybeFlatMapIterableObservable<T, U>(this, mapper));
     }
 
@@ -3691,6 +3705,9 @@ public final Disposable subscribe(Consumer<? super T> onSuccess, Consumer<? supe
     @SchedulerSupport(SchedulerSupport.NONE)
     public final Disposable subscribe(Consumer<? super T> onSuccess, Consumer<? super Throwable> onError,
             Action onComplete) {
+        ObjectHelper.requireNonNull(onSuccess, "onSuccess is null");
+        ObjectHelper.requireNonNull(onError, "onError is null");
+        ObjectHelper.requireNonNull(onComplete, "onComplete is null");
         return subscribeWith(new MaybeCallbackObserver<T>(onSuccess, onError, onComplete));
     }
 
diff --git a/src/main/java/io/reactivex/Observable.java b/src/main/java/io/reactivex/Observable.java
index e1361a22fe..7457fcd2de 100644
--- a/src/main/java/io/reactivex/Observable.java
+++ b/src/main/java/io/reactivex/Observable.java
@@ -371,6 +371,8 @@ public static <T, R> Observable<R> combineLatest(ObservableSource<? extends T>[]
     public static <T1, T2, R> Observable<R> combineLatest(
             ObservableSource<? extends T1> source1, ObservableSource<? extends T2> source2,
             BiFunction<? super T1, ? super T2, ? extends R> combiner) {
+        ObjectHelper.requireNonNull(source1, "source1 is null");
+        ObjectHelper.requireNonNull(source2, "source2 is null");
         return combineLatest(Functions.toFunction(combiner), bufferSize(), source1, source2);
     }
 
@@ -412,6 +414,9 @@ public static <T1, T2, T3, R> Observable<R> combineLatest(
             ObservableSource<? extends T1> source1, ObservableSource<? extends T2> source2,
             ObservableSource<? extends T3> source3,
             Function3<? super T1, ? super T2, ? super T3, ? extends R> combiner) {
+        ObjectHelper.requireNonNull(source1, "source1 is null");
+        ObjectHelper.requireNonNull(source2, "source2 is null");
+        ObjectHelper.requireNonNull(source3, "source3 is null");
         return combineLatest(Functions.toFunction(combiner), bufferSize(), source1, source2, source3);
     }
 
@@ -456,6 +461,10 @@ public static <T1, T2, T3, T4, R> Observable<R> combineLatest(
             ObservableSource<? extends T1> source1, ObservableSource<? extends T2> source2,
             ObservableSource<? extends T3> source3, ObservableSource<? extends T4> source4,
             Function4<? super T1, ? super T2, ? super T3, ? super T4, ? extends R> combiner) {
+        ObjectHelper.requireNonNull(source1, "source1 is null");
+        ObjectHelper.requireNonNull(source2, "source2 is null");
+        ObjectHelper.requireNonNull(source3, "source3 is null");
+        ObjectHelper.requireNonNull(source4, "source4 is null");
         return combineLatest(Functions.toFunction(combiner), bufferSize(), source1, source2, source3, source4);
     }
 
@@ -504,6 +513,11 @@ public static <T1, T2, T3, T4, T5, R> Observable<R> combineLatest(
             ObservableSource<? extends T3> source3, ObservableSource<? extends T4> source4,
             ObservableSource<? extends T5> source5,
             Function5<? super T1, ? super T2, ? super T3, ? super T4, ? super T5, ? extends R> combiner) {
+        ObjectHelper.requireNonNull(source1, "source1 is null");
+        ObjectHelper.requireNonNull(source2, "source2 is null");
+        ObjectHelper.requireNonNull(source3, "source3 is null");
+        ObjectHelper.requireNonNull(source4, "source4 is null");
+        ObjectHelper.requireNonNull(source5, "source5 is null");
         return combineLatest(Functions.toFunction(combiner), bufferSize(), source1, source2, source3, source4, source5);
     }
 
@@ -555,6 +569,12 @@ public static <T1, T2, T3, T4, T5, T6, R> Observable<R> combineLatest(
             ObservableSource<? extends T3> source3, ObservableSource<? extends T4> source4,
             ObservableSource<? extends T5> source5, ObservableSource<? extends T6> source6,
             Function6<? super T1, ? super T2, ? super T3, ? super T4, ? super T5, ? super T6, ? extends R> combiner) {
+        ObjectHelper.requireNonNull(source1, "source1 is null");
+        ObjectHelper.requireNonNull(source2, "source2 is null");
+        ObjectHelper.requireNonNull(source3, "source3 is null");
+        ObjectHelper.requireNonNull(source4, "source4 is null");
+        ObjectHelper.requireNonNull(source5, "source5 is null");
+        ObjectHelper.requireNonNull(source6, "source6 is null");
         return combineLatest(Functions.toFunction(combiner), bufferSize(), source1, source2, source3, source4, source5, source6);
     }
 
@@ -610,6 +630,13 @@ public static <T1, T2, T3, T4, T5, T6, T7, R> Observable<R> combineLatest(
             ObservableSource<? extends T5> source5, ObservableSource<? extends T6> source6,
             ObservableSource<? extends T7> source7,
             Function7<? super T1, ? super T2, ? super T3, ? super T4, ? super T5, ? super T6, ? super T7, ? extends R> combiner) {
+        ObjectHelper.requireNonNull(source1, "source1 is null");
+        ObjectHelper.requireNonNull(source2, "source2 is null");
+        ObjectHelper.requireNonNull(source3, "source3 is null");
+        ObjectHelper.requireNonNull(source4, "source4 is null");
+        ObjectHelper.requireNonNull(source5, "source5 is null");
+        ObjectHelper.requireNonNull(source6, "source6 is null");
+        ObjectHelper.requireNonNull(source7, "source7 is null");
         return combineLatest(Functions.toFunction(combiner), bufferSize(), source1, source2, source3, source4, source5, source6, source7);
     }
 
@@ -668,6 +695,14 @@ public static <T1, T2, T3, T4, T5, T6, T7, T8, R> Observable<R> combineLatest(
             ObservableSource<? extends T5> source5, ObservableSource<? extends T6> source6,
             ObservableSource<? extends T7> source7, ObservableSource<? extends T8> source8,
             Function8<? super T1, ? super T2, ? super T3, ? super T4, ? super T5, ? super T6, ? super T7, ? super T8, ? extends R> combiner) {
+        ObjectHelper.requireNonNull(source1, "source1 is null");
+        ObjectHelper.requireNonNull(source2, "source2 is null");
+        ObjectHelper.requireNonNull(source3, "source3 is null");
+        ObjectHelper.requireNonNull(source4, "source4 is null");
+        ObjectHelper.requireNonNull(source5, "source5 is null");
+        ObjectHelper.requireNonNull(source6, "source6 is null");
+        ObjectHelper.requireNonNull(source7, "source7 is null");
+        ObjectHelper.requireNonNull(source8, "source8 is null");
         return combineLatest(Functions.toFunction(combiner), bufferSize(), source1, source2, source3, source4, source5, source6, source7, source8);
     }
 
@@ -730,6 +765,15 @@ public static <T1, T2, T3, T4, T5, T6, T7, T8, T9, R> Observable<R> combineLates
             ObservableSource<? extends T7> source7, ObservableSource<? extends T8> source8,
             ObservableSource<? extends T9> source9,
             Function9<? super T1, ? super T2, ? super T3, ? super T4, ? super T5, ? super T6, ? super T7, ? super T8, ? super T9, ? extends R> combiner) {
+        ObjectHelper.requireNonNull(source1, "source1 is null");
+        ObjectHelper.requireNonNull(source2, "source2 is null");
+        ObjectHelper.requireNonNull(source3, "source3 is null");
+        ObjectHelper.requireNonNull(source4, "source4 is null");
+        ObjectHelper.requireNonNull(source5, "source5 is null");
+        ObjectHelper.requireNonNull(source6, "source6 is null");
+        ObjectHelper.requireNonNull(source7, "source7 is null");
+        ObjectHelper.requireNonNull(source8, "source8 is null");
+        ObjectHelper.requireNonNull(source9, "source9 is null");
         return combineLatest(Functions.toFunction(combiner), bufferSize(), source1, source2, source3, source4, source5, source6, source7, source8, source9);
     }
 
@@ -1012,6 +1056,7 @@ public static <T> Observable<T> concat(ObservableSource<? extends ObservableSour
     @SchedulerSupport(SchedulerSupport.NONE)
     public static <T> Observable<T> concat(ObservableSource<? extends ObservableSource<? extends T>> sources, int prefetch) {
         ObjectHelper.requireNonNull(sources, "sources is null");
+        ObjectHelper.verifyPositive(prefetch, "prefetch");
         return RxJavaPlugins.onAssembly(new ObservableConcatMap(sources, Functions.identity(), prefetch, ErrorMode.IMMEDIATE));
     }
 
@@ -1038,6 +1083,8 @@ public static <T> Observable<T> concat(ObservableSource<? extends ObservableSour
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     public static <T> Observable<T> concat(ObservableSource<? extends T> source1, ObservableSource<? extends T> source2) {
+        ObjectHelper.requireNonNull(source1, "source1 is null");
+        ObjectHelper.requireNonNull(source2, "source2 is null");
         return concatArray(source1, source2);
     }
 
@@ -1068,6 +1115,9 @@ public static <T> Observable<T> concat(ObservableSource<? extends T> source1, Ob
     public static <T> Observable<T> concat(
             ObservableSource<? extends T> source1, ObservableSource<? extends T> source2,
             ObservableSource<? extends T> source3) {
+        ObjectHelper.requireNonNull(source1, "source1 is null");
+        ObjectHelper.requireNonNull(source2, "source2 is null");
+        ObjectHelper.requireNonNull(source3, "source3 is null");
         return concatArray(source1, source2, source3);
     }
 
@@ -1100,6 +1150,10 @@ public static <T> Observable<T> concat(
     public static <T> Observable<T> concat(
             ObservableSource<? extends T> source1, ObservableSource<? extends T> source2,
             ObservableSource<? extends T> source3, ObservableSource<? extends T> source4) {
+        ObjectHelper.requireNonNull(source1, "source1 is null");
+        ObjectHelper.requireNonNull(source2, "source2 is null");
+        ObjectHelper.requireNonNull(source3, "source3 is null");
+        ObjectHelper.requireNonNull(source4, "source4 is null");
         return concatArray(source1, source2, source3, source4);
     }
 
@@ -1268,6 +1322,8 @@ public static <T> Observable<T> concatDelayError(ObservableSource<? extends Obse
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     public static <T> Observable<T> concatDelayError(ObservableSource<? extends ObservableSource<? extends T>> sources, int prefetch, boolean tillTheEnd) {
+        ObjectHelper.requireNonNull(sources, "sources is null");
+        ObjectHelper.verifyPositive(prefetch, "prefetch is null");
         return RxJavaPlugins.onAssembly(new ObservableConcatMap(sources, Functions.identity(), prefetch, tillTheEnd ? ErrorMode.END : ErrorMode.BOUNDARY));
     }
 
@@ -1318,6 +1374,8 @@ public static <T> Observable<T> concatEager(ObservableSource<? extends Observabl
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     public static <T> Observable<T> concatEager(ObservableSource<? extends ObservableSource<? extends T>> sources, int maxConcurrency, int prefetch) {
+        ObjectHelper.requireNonNull(maxConcurrency, "maxConcurrency is null");
+        ObjectHelper.requireNonNull(prefetch, "prefetch is null");
         return wrap(sources).concatMapEager((Function)Functions.identity(), maxConcurrency, prefetch);
     }
 
@@ -1368,6 +1426,8 @@ public static <T> Observable<T> concatEager(Iterable<? extends ObservableSource<
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     public static <T> Observable<T> concatEager(Iterable<? extends ObservableSource<? extends T>> sources, int maxConcurrency, int prefetch) {
+        ObjectHelper.requireNonNull(maxConcurrency, "maxConcurrency is null");
+        ObjectHelper.requireNonNull(prefetch, "prefetch is null");
         return fromIterable(sources).concatMapEagerDelayError((Function)Functions.identity(), maxConcurrency, prefetch, false);
     }
 
@@ -2617,6 +2677,7 @@ public static <T> Observable<T> merge(Iterable<? extends ObservableSource<? exte
     @SchedulerSupport(SchedulerSupport.NONE)
     @SuppressWarnings({ "unchecked", "rawtypes" })
     public static <T> Observable<T> merge(ObservableSource<? extends ObservableSource<? extends T>> sources) {
+        ObjectHelper.requireNonNull(sources, "sources is null");
         return RxJavaPlugins.onAssembly(new ObservableFlatMap(sources, Functions.identity(), false, Integer.MAX_VALUE, bufferSize()));
     }
 
@@ -2650,6 +2711,8 @@ public static <T> Observable<T> merge(ObservableSource<? extends ObservableSourc
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     public static <T> Observable<T> merge(ObservableSource<? extends ObservableSource<? extends T>> sources, int maxConcurrency) {
+        ObjectHelper.requireNonNull(sources, "sources is null");
+        ObjectHelper.verifyPositive(maxConcurrency, "maxConcurrency");
         return RxJavaPlugins.onAssembly(new ObservableFlatMap(sources, Functions.identity(), false, maxConcurrency, bufferSize()));
     }
 
@@ -2943,6 +3006,7 @@ public static <T> Observable<T> mergeDelayError(Iterable<? extends ObservableSou
     @SchedulerSupport(SchedulerSupport.NONE)
     @SuppressWarnings({ "unchecked", "rawtypes" })
     public static <T> Observable<T> mergeDelayError(ObservableSource<? extends ObservableSource<? extends T>> sources) {
+        ObjectHelper.requireNonNull(sources, "sources is null");
         return RxJavaPlugins.onAssembly(new ObservableFlatMap(sources, Functions.identity(), true, Integer.MAX_VALUE, bufferSize()));
     }
 
@@ -2979,6 +3043,8 @@ public static <T> Observable<T> mergeDelayError(ObservableSource<? extends Obser
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     public static <T> Observable<T> mergeDelayError(ObservableSource<? extends ObservableSource<? extends T>> sources, int maxConcurrency) {
+        ObjectHelper.requireNonNull(sources, "sources is null");
+        ObjectHelper.verifyPositive(maxConcurrency, "maxConcurrency");
         return RxJavaPlugins.onAssembly(new ObservableFlatMap(sources, Functions.identity(), true, maxConcurrency, bufferSize()));
     }
 
@@ -3385,6 +3451,7 @@ public static <T> Single<Boolean> sequenceEqual(ObservableSource<? extends T> so
     @SchedulerSupport(SchedulerSupport.NONE)
     public static <T> Observable<T> switchOnNext(ObservableSource<? extends ObservableSource<? extends T>> sources, int bufferSize) {
         ObjectHelper.requireNonNull(sources, "sources is null");
+        ObjectHelper.verifyPositive(bufferSize, "bufferSize");
         return RxJavaPlugins.onAssembly(new ObservableSwitchMap(sources, Functions.identity(), bufferSize, false));
     }
 
@@ -3809,6 +3876,8 @@ public static <T, R> Observable<R> zip(ObservableSource<? extends ObservableSour
     public static <T1, T2, R> Observable<R> zip(
             ObservableSource<? extends T1> source1, ObservableSource<? extends T2> source2,
             BiFunction<? super T1, ? super T2, ? extends R> zipper) {
+        ObjectHelper.requireNonNull(source1, "source1 is null");
+        ObjectHelper.requireNonNull(source2, "source2 is null");
         return zipArray(Functions.toFunction(zipper), false, bufferSize(), source1, source2);
     }
 
@@ -3863,6 +3932,8 @@ public static <T1, T2, R> Observable<R> zip(
     public static <T1, T2, R> Observable<R> zip(
             ObservableSource<? extends T1> source1, ObservableSource<? extends T2> source2,
             BiFunction<? super T1, ? super T2, ? extends R> zipper, boolean delayError) {
+        ObjectHelper.requireNonNull(source1, "source1 is null");
+        ObjectHelper.requireNonNull(source2, "source2 is null");
         return zipArray(Functions.toFunction(zipper), delayError, bufferSize(), source1, source2);
     }
 
@@ -3918,6 +3989,8 @@ public static <T1, T2, R> Observable<R> zip(
     public static <T1, T2, R> Observable<R> zip(
             ObservableSource<? extends T1> source1, ObservableSource<? extends T2> source2,
             BiFunction<? super T1, ? super T2, ? extends R> zipper, boolean delayError, int bufferSize) {
+        ObjectHelper.requireNonNull(source1, "source1 is null");
+        ObjectHelper.requireNonNull(source2, "source2 is null");
         return zipArray(Functions.toFunction(zipper), delayError, bufferSize, source1, source2);
     }
 
@@ -3975,6 +4048,9 @@ public static <T1, T2, R> Observable<R> zip(
     public static <T1, T2, T3, R> Observable<R> zip(
             ObservableSource<? extends T1> source1, ObservableSource<? extends T2> source2, ObservableSource<? extends T3> source3,
             Function3<? super T1, ? super T2, ? super T3, ? extends R> zipper) {
+        ObjectHelper.requireNonNull(source1, "source1 is null");
+        ObjectHelper.requireNonNull(source2, "source2 is null");
+        ObjectHelper.requireNonNull(source3, "source3 is null");
         return zipArray(Functions.toFunction(zipper), false, bufferSize(), source1, source2, source3);
     }
 
@@ -4036,6 +4112,10 @@ public static <T1, T2, T3, T4, R> Observable<R> zip(
             ObservableSource<? extends T1> source1, ObservableSource<? extends T2> source2, ObservableSource<? extends T3> source3,
             ObservableSource<? extends T4> source4,
             Function4<? super T1, ? super T2, ? super T3, ? super T4, ? extends R> zipper) {
+        ObjectHelper.requireNonNull(source1, "source1 is null");
+        ObjectHelper.requireNonNull(source2, "source2 is null");
+        ObjectHelper.requireNonNull(source3, "source3 is null");
+        ObjectHelper.requireNonNull(source4, "source4 is null");
         return zipArray(Functions.toFunction(zipper), false, bufferSize(), source1, source2, source3, source4);
     }
 
@@ -4100,6 +4180,11 @@ public static <T1, T2, T3, T4, T5, R> Observable<R> zip(
             ObservableSource<? extends T1> source1, ObservableSource<? extends T2> source2, ObservableSource<? extends T3> source3,
             ObservableSource<? extends T4> source4, ObservableSource<? extends T5> source5,
             Function5<? super T1, ? super T2, ? super T3, ? super T4, ? super T5, ? extends R> zipper) {
+        ObjectHelper.requireNonNull(source1, "source1 is null");
+        ObjectHelper.requireNonNull(source2, "source2 is null");
+        ObjectHelper.requireNonNull(source3, "source3 is null");
+        ObjectHelper.requireNonNull(source4, "source4 is null");
+        ObjectHelper.requireNonNull(source5, "source5 is null");
         return zipArray(Functions.toFunction(zipper), false, bufferSize(), source1, source2, source3, source4, source5);
     }
 
@@ -4166,6 +4251,12 @@ public static <T1, T2, T3, T4, T5, T6, R> Observable<R> zip(
             ObservableSource<? extends T1> source1, ObservableSource<? extends T2> source2, ObservableSource<? extends T3> source3,
             ObservableSource<? extends T4> source4, ObservableSource<? extends T5> source5, ObservableSource<? extends T6> source6,
             Function6<? super T1, ? super T2, ? super T3, ? super T4, ? super T5, ? super T6, ? extends R> zipper) {
+        ObjectHelper.requireNonNull(source1, "source1 is null");
+        ObjectHelper.requireNonNull(source2, "source2 is null");
+        ObjectHelper.requireNonNull(source3, "source3 is null");
+        ObjectHelper.requireNonNull(source4, "source4 is null");
+        ObjectHelper.requireNonNull(source5, "source5 is null");
+        ObjectHelper.requireNonNull(source6, "source6 is null");
         return zipArray(Functions.toFunction(zipper), false, bufferSize(), source1, source2, source3, source4, source5, source6);
     }
 
@@ -4236,6 +4327,13 @@ public static <T1, T2, T3, T4, T5, T6, T7, R> Observable<R> zip(
             ObservableSource<? extends T4> source4, ObservableSource<? extends T5> source5, ObservableSource<? extends T6> source6,
             ObservableSource<? extends T7> source7,
             Function7<? super T1, ? super T2, ? super T3, ? super T4, ? super T5, ? super T6, ? super T7, ? extends R> zipper) {
+        ObjectHelper.requireNonNull(source1, "source1 is null");
+        ObjectHelper.requireNonNull(source2, "source2 is null");
+        ObjectHelper.requireNonNull(source3, "source3 is null");
+        ObjectHelper.requireNonNull(source4, "source4 is null");
+        ObjectHelper.requireNonNull(source5, "source5 is null");
+        ObjectHelper.requireNonNull(source6, "source6 is null");
+        ObjectHelper.requireNonNull(source7, "source7 is null");
         return zipArray(Functions.toFunction(zipper), false, bufferSize(), source1, source2, source3, source4, source5, source6, source7);
     }
 
@@ -4309,6 +4407,14 @@ public static <T1, T2, T3, T4, T5, T6, T7, T8, R> Observable<R> zip(
             ObservableSource<? extends T4> source4, ObservableSource<? extends T5> source5, ObservableSource<? extends T6> source6,
             ObservableSource<? extends T7> source7, ObservableSource<? extends T8> source8,
             Function8<? super T1, ? super T2, ? super T3, ? super T4, ? super T5, ? super T6, ? super T7, ? super T8, ? extends R> zipper) {
+        ObjectHelper.requireNonNull(source1, "source1 is null");
+        ObjectHelper.requireNonNull(source2, "source2 is null");
+        ObjectHelper.requireNonNull(source3, "source3 is null");
+        ObjectHelper.requireNonNull(source4, "source4 is null");
+        ObjectHelper.requireNonNull(source5, "source5 is null");
+        ObjectHelper.requireNonNull(source6, "source6 is null");
+        ObjectHelper.requireNonNull(source7, "source7 is null");
+        ObjectHelper.requireNonNull(source8, "source8 is null");
         return zipArray(Functions.toFunction(zipper), false, bufferSize(), source1, source2, source3, source4, source5, source6, source7, source8);
     }
 
@@ -4385,6 +4491,15 @@ public static <T1, T2, T3, T4, T5, T6, T7, T8, T9, R> Observable<R> zip(
             ObservableSource<? extends T4> source4, ObservableSource<? extends T5> source5, ObservableSource<? extends T6> source6,
             ObservableSource<? extends T7> source7, ObservableSource<? extends T8> source8, ObservableSource<? extends T9> source9,
             Function9<? super T1, ? super T2, ? super T3, ? super T4, ? super T5, ? super T6, ? super T7, ? super T8, ? super T9, ? extends R> zipper) {
+        ObjectHelper.requireNonNull(source1, "source1 is null");
+        ObjectHelper.requireNonNull(source2, "source2 is null");
+        ObjectHelper.requireNonNull(source3, "source3 is null");
+        ObjectHelper.requireNonNull(source4, "source4 is null");
+        ObjectHelper.requireNonNull(source5, "source5 is null");
+        ObjectHelper.requireNonNull(source6, "source6 is null");
+        ObjectHelper.requireNonNull(source7, "source7 is null");
+        ObjectHelper.requireNonNull(source8, "source8 is null");
+        ObjectHelper.requireNonNull(source9, "source9 is null");
         return zipArray(Functions.toFunction(zipper), false, bufferSize(), source1, source2, source3, source4, source5, source6, source7, source8, source9);
     }
 
@@ -5490,6 +5605,7 @@ public final <B> Observable<List<T>> buffer(ObservableSource<B> boundary) {
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     public final <B> Observable<List<T>> buffer(ObservableSource<B> boundary, final int initialCapacity) {
+        ObjectHelper.verifyPositive(initialCapacity, "initialCapacity");
         return buffer(boundary, Functions.<T>createArrayList(initialCapacity));
     }
 
@@ -5915,6 +6031,7 @@ public final <R> Observable<R> concatMapDelayError(Function<? super T, ? extends
     @SchedulerSupport(SchedulerSupport.NONE)
     public final <R> Observable<R> concatMapDelayError(Function<? super T, ? extends ObservableSource<? extends R>> mapper,
             int prefetch, boolean tillTheEnd) {
+        ObjectHelper.requireNonNull(mapper, "mapper is null");
         ObjectHelper.verifyPositive(prefetch, "prefetch");
         if (this instanceof ScalarCallable) {
             @SuppressWarnings("unchecked")
@@ -6034,6 +6151,9 @@ public final <R> Observable<R> concatMapEagerDelayError(Function<? super T, ? ex
     @SchedulerSupport(SchedulerSupport.NONE)
     public final <R> Observable<R> concatMapEagerDelayError(Function<? super T, ? extends ObservableSource<? extends R>> mapper,
             int maxConcurrency, int prefetch, boolean tillTheEnd) {
+        ObjectHelper.requireNonNull(mapper, "mapper is null");
+        ObjectHelper.verifyPositive(maxConcurrency, "maxConcurrency");
+        ObjectHelper.verifyPositive(prefetch, "prefetch");
         return RxJavaPlugins.onAssembly(new ObservableConcatMapEager<T, R>(this, mapper, tillTheEnd ? ErrorMode.END : ErrorMode.BOUNDARY, maxConcurrency, prefetch));
     }
 
@@ -6087,6 +6207,8 @@ public final <U> Observable<U> concatMapIterable(final Function<? super T, ? ext
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     public final <U> Observable<U> concatMapIterable(final Function<? super T, ? extends Iterable<? extends U>> mapper, int prefetch) {
+        ObjectHelper.requireNonNull(mapper, "mapper is null");
+        ObjectHelper.verifyPositive(prefetch, "prefetch");
         return concatMap(ObservableInternalHelper.flatMapIntoIterable(mapper), prefetch);
     }
 
@@ -7681,6 +7803,8 @@ public final <U> Observable<U> flatMapIterable(final Function<? super T, ? exten
     @SchedulerSupport(SchedulerSupport.NONE)
     public final <U, V> Observable<V> flatMapIterable(final Function<? super T, ? extends Iterable<? extends U>> mapper,
             BiFunction<? super T, ? super U, ? extends V> resultSelector) {
+        ObjectHelper.requireNonNull(mapper, "mapper is null");
+        ObjectHelper.requireNonNull(resultSelector, "resultSelector is null");
         return flatMap(ObservableInternalHelper.flatMapIntoIterable(mapper), resultSelector, false, bufferSize(), bufferSize());
     }
 
@@ -8112,6 +8236,10 @@ public final <TRight, TLeftEnd, TRightEnd, R> Observable<R> groupJoin(
             Function<? super TRight, ? extends ObservableSource<TRightEnd>> rightEnd,
             BiFunction<? super T, ? super Observable<TRight>, ? extends R> resultSelector
                     ) {
+        ObjectHelper.requireNonNull(other, "other is null");
+        ObjectHelper.requireNonNull(leftEnd, "leftEnd is null");
+        ObjectHelper.requireNonNull(rightEnd, "rightEnd is null");
+        ObjectHelper.requireNonNull(resultSelector, "resultSelector is null");
         return RxJavaPlugins.onAssembly(new ObservableGroupJoin<T, TRight, TLeftEnd, TRightEnd, R>(
                 this, other, leftEnd, rightEnd, resultSelector));
     }
@@ -8213,6 +8341,10 @@ public final <TRight, TLeftEnd, TRightEnd, R> Observable<R> join(
             Function<? super TRight, ? extends ObservableSource<TRightEnd>> rightEnd,
             BiFunction<? super T, ? super TRight, ? extends R> resultSelector
                     ) {
+        ObjectHelper.requireNonNull(other, "other is null");
+        ObjectHelper.requireNonNull(leftEnd, "leftEnd is null");
+        ObjectHelper.requireNonNull(rightEnd, "rightEnd is null");
+        ObjectHelper.requireNonNull(resultSelector, "resultSelector is null");
         return RxJavaPlugins.onAssembly(new ObservableJoin<T, TRight, TLeftEnd, TRightEnd, R>(
                 this, other, leftEnd, rightEnd, resultSelector));
     }
@@ -9046,6 +9178,7 @@ public final <R> Observable<R> replay(Function<? super Observable<T>, ? extends
     @SchedulerSupport(SchedulerSupport.NONE)
     public final <R> Observable<R> replay(Function<? super Observable<T>, ? extends ObservableSource<R>> selector, final int bufferSize) {
         ObjectHelper.requireNonNull(selector, "selector is null");
+        ObjectHelper.verifyPositive(bufferSize, "bufferSize");
         return ObservableReplay.multicastSelector(ObservableInternalHelper.replayCallable(this, bufferSize), selector);
     }
 
@@ -9118,8 +9251,10 @@ public final <R> Observable<R> replay(Function<? super Observable<T>, ? extends
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.CUSTOM)
     public final <R> Observable<R> replay(Function<? super Observable<T>, ? extends ObservableSource<R>> selector, final int bufferSize, final long time, final TimeUnit unit, final Scheduler scheduler) {
-        ObjectHelper.verifyPositive(bufferSize, "bufferSize");
         ObjectHelper.requireNonNull(selector, "selector is null");
+        ObjectHelper.verifyPositive(bufferSize, "bufferSize");
+        ObjectHelper.requireNonNull(unit, "unit is null");
+        ObjectHelper.requireNonNull(scheduler, "scheduler is null");
         return ObservableReplay.multicastSelector(
                 ObservableInternalHelper.replayCallable(this, bufferSize, time, unit, scheduler), selector);
     }
@@ -9152,6 +9287,9 @@ public final <R> Observable<R> replay(Function<? super Observable<T>, ? extends
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.CUSTOM)
     public final <R> Observable<R> replay(final Function<? super Observable<T>, ? extends ObservableSource<R>> selector, final int bufferSize, final Scheduler scheduler) {
+        ObjectHelper.requireNonNull(selector, "selector is null");
+        ObjectHelper.requireNonNull(scheduler, "scheduler is null");
+        ObjectHelper.verifyPositive(bufferSize, "bufferSize");
         return ObservableReplay.multicastSelector(ObservableInternalHelper.replayCallable(this, bufferSize),
                 ObservableInternalHelper.replayFunction(selector, scheduler));
     }
@@ -9275,6 +9413,7 @@ public final <R> Observable<R> replay(final Function<? super Observable<T>, ? ex
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     public final ConnectableObservable<T> replay(final int bufferSize) {
+        ObjectHelper.verifyPositive(bufferSize, "bufferSize");
         return ObservableReplay.create(this, bufferSize);
     }
 
@@ -9366,6 +9505,7 @@ public final ConnectableObservable<T> replay(final int bufferSize, final long ti
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.CUSTOM)
     public final ConnectableObservable<T> replay(final int bufferSize, final Scheduler scheduler) {
+        ObjectHelper.verifyPositive(bufferSize, "bufferSize");
         return ObservableReplay.observeOn(replay(bufferSize), scheduler);
     }
 
@@ -10443,6 +10583,7 @@ public final Observable<T> sorted() {
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     public final Observable<T> sorted(Comparator<? super T> sortFunction) {
+        ObjectHelper.requireNonNull(sortFunction, "sortFunction is null");
         return toList().toObservable().map(Functions.listSorter(sortFunction)).flatMapIterable(Functions.<List<T>>identity());
     }
 
@@ -12208,6 +12349,7 @@ public final <U extends Collection<? super T>> Single<U> toList(Callable<U> coll
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     public final <K> Single<Map<K, T>> toMap(final Function<? super T, ? extends K> keySelector) {
+        ObjectHelper.requireNonNull(keySelector, "keySelector is null");
         return collect(HashMapSupplier.<K, T>asCallable(), Functions.toMapKeySelector(keySelector));
     }
 
@@ -12272,6 +12414,10 @@ public final <K, V> Single<Map<K, V>> toMap(
             final Function<? super T, ? extends K> keySelector,
             final Function<? super T, ? extends V> valueSelector,
             Callable<? extends Map<K, V>> mapSupplier) {
+        ObjectHelper.requireNonNull(keySelector, "keySelector is null");
+        ObjectHelper.requireNonNull(keySelector, "keySelector is null");
+        ObjectHelper.requireNonNull(valueSelector, "valueSelector is null");
+        ObjectHelper.requireNonNull(mapSupplier, "mapSupplier is null");
         return collect(mapSupplier, Functions.toMapKeyValueSelector(keySelector, valueSelector));
     }
 
@@ -13028,6 +13174,7 @@ public final <B> Observable<Observable<T>> window(ObservableSource<B> boundary)
     @SchedulerSupport(SchedulerSupport.NONE)
     public final <B> Observable<Observable<T>> window(ObservableSource<B> boundary, int bufferSize) {
         ObjectHelper.requireNonNull(boundary, "boundary is null");
+        ObjectHelper.verifyPositive(bufferSize, "bufferSize");
         return RxJavaPlugins.onAssembly(new ObservableWindowBoundary<T, B>(this, boundary, bufferSize));
     }
 
@@ -13094,6 +13241,7 @@ public final <U, V> Observable<Observable<T>> window(
             Function<? super U, ? extends ObservableSource<V>> closingIndicator, int bufferSize) {
         ObjectHelper.requireNonNull(openingIndicator, "openingIndicator is null");
         ObjectHelper.requireNonNull(closingIndicator, "closingIndicator is null");
+        ObjectHelper.verifyPositive(bufferSize, "bufferSize");
         return RxJavaPlugins.onAssembly(new ObservableWindowBoundarySelector<T, U, V>(this, openingIndicator, closingIndicator, bufferSize));
     }
 
@@ -13150,6 +13298,7 @@ public final <B> Observable<Observable<T>> window(Callable<? extends ObservableS
     @SchedulerSupport(SchedulerSupport.NONE)
     public final <B> Observable<Observable<T>> window(Callable<? extends ObservableSource<B>> boundary, int bufferSize) {
         ObjectHelper.requireNonNull(boundary, "boundary is null");
+        ObjectHelper.verifyPositive(bufferSize, "bufferSize");
         return RxJavaPlugins.onAssembly(new ObservableWindowBoundarySupplier<T, B>(this, boundary, bufferSize));
     }
 
diff --git a/src/main/java/io/reactivex/Single.java b/src/main/java/io/reactivex/Single.java
index bb42de50f0..f516143c72 100644
--- a/src/main/java/io/reactivex/Single.java
+++ b/src/main/java/io/reactivex/Single.java
@@ -142,6 +142,7 @@ public static <T> Flowable<T> concat(Iterable<? extends SingleSource<? extends T
     @SchedulerSupport(SchedulerSupport.NONE)
     @SuppressWarnings({ "unchecked", "rawtypes" })
     public static <T> Observable<T> concat(ObservableSource<? extends SingleSource<? extends T>> sources) {
+        ObjectHelper.requireNonNull(sources, "sources is null");
         return RxJavaPlugins.onAssembly(new ObservableConcatMap(sources, SingleInternalHelper.toObservable(), 2, ErrorMode.IMMEDIATE));
     }
 
@@ -685,6 +686,7 @@ public static <T> Flowable<T> merge(Iterable<? extends SingleSource<? extends T>
     @SchedulerSupport(SchedulerSupport.NONE)
     @SuppressWarnings({ "unchecked", "rawtypes" })
     public static <T> Flowable<T> merge(Publisher<? extends SingleSource<? extends T>> sources) {
+        ObjectHelper.requireNonNull(sources, "sources is null");
         return RxJavaPlugins.onAssembly(new FlowableFlatMapPublisher(sources, SingleInternalHelper.toFlowable(), false, Integer.MAX_VALUE, Flowable.bufferSize()));
     }
 
@@ -1669,6 +1671,7 @@ public final Single<T> delay(final long time, final TimeUnit unit, final Schedul
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     public final Single<T> delaySubscription(CompletableSource other) {
+        ObjectHelper.requireNonNull(other, "other is null");
         return RxJavaPlugins.onAssembly(new SingleDelayWithCompletable<T>(this, other));
     }
 
@@ -1690,6 +1693,7 @@ public final Single<T> delaySubscription(CompletableSource other) {
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     public final <U> Single<T> delaySubscription(SingleSource<U> other) {
+        ObjectHelper.requireNonNull(other, "other is null");
         return RxJavaPlugins.onAssembly(new SingleDelayWithSingle<T, U>(this, other));
     }
 
@@ -1711,6 +1715,7 @@ public final <U> Single<T> delaySubscription(SingleSource<U> other) {
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     public final <U> Single<T> delaySubscription(ObservableSource<U> other) {
+        ObjectHelper.requireNonNull(other, "other is null");
         return RxJavaPlugins.onAssembly(new SingleDelayWithObservable<T, U>(this, other));
     }
 
@@ -1737,6 +1742,7 @@ public final <U> Single<T> delaySubscription(ObservableSource<U> other) {
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     public final <U> Single<T> delaySubscription(Publisher<U> other) {
+        ObjectHelper.requireNonNull(other, "other is null");
         return RxJavaPlugins.onAssembly(new SingleDelayWithPublisher<T, U>(this, other));
     }
 
@@ -2059,6 +2065,7 @@ public final <R> Flowable<R> flatMapPublisher(Function<? super T, ? extends Publ
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     public final <U> Flowable<U> flattenAsFlowable(final Function<? super T, ? extends Iterable<? extends U>> mapper) {
+        ObjectHelper.requireNonNull(mapper, "mapper is null");
         return RxJavaPlugins.onAssembly(new SingleFlatMapIterableFlowable<T, U>(this, mapper));
     }
 
@@ -2082,6 +2089,7 @@ public final <U> Flowable<U> flattenAsFlowable(final Function<? super T, ? exten
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     public final <U> Observable<U> flattenAsObservable(final Function<? super T, ? extends Iterable<? extends U>> mapper) {
+        ObjectHelper.requireNonNull(mapper, "mapper is null");
         return RxJavaPlugins.onAssembly(new SingleFlatMapIterableObservable<T, U>(this, mapper));
     }
 
@@ -2197,6 +2205,7 @@ public final <R> Single<R> lift(final SingleOperator<? extends R, ? super T> lif
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     public final <R> Single<R> map(Function<? super T, ? extends R> mapper) {
+        ObjectHelper.requireNonNull(mapper, "mapper is null");
         return RxJavaPlugins.onAssembly(new SingleMap<T, R>(this, mapper));
     }
 
@@ -2781,6 +2790,7 @@ public final Single<T> subscribeOn(final Scheduler scheduler) {
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     public final Single<T> takeUntil(final CompletableSource other) {
+        ObjectHelper.requireNonNull(other, "other is null");
         return takeUntil(new CompletableToFlowable<T>(other));
     }
 
@@ -2811,6 +2821,7 @@ public final Single<T> takeUntil(final CompletableSource other) {
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     public final <E> Single<T> takeUntil(final Publisher<E> other) {
+        ObjectHelper.requireNonNull(other, "other is null");
         return RxJavaPlugins.onAssembly(new SingleTakeUntil<T, E>(this, other));
     }
 
@@ -2835,6 +2846,7 @@ public final <E> Single<T> takeUntil(final Publisher<E> other) {
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     public final <E> Single<T> takeUntil(final SingleSource<? extends E> other) {
+        ObjectHelper.requireNonNull(other, "other is null");
         return takeUntil(new SingleToFlowable<E>(other));
     }
 
diff --git a/src/main/java/io/reactivex/internal/operators/flowable/FlowableBlockingSubscribe.java b/src/main/java/io/reactivex/internal/operators/flowable/FlowableBlockingSubscribe.java
index 24ece91821..d79c6f3061 100644
--- a/src/main/java/io/reactivex/internal/operators/flowable/FlowableBlockingSubscribe.java
+++ b/src/main/java/io/reactivex/internal/operators/flowable/FlowableBlockingSubscribe.java
@@ -18,7 +18,7 @@
 import org.reactivestreams.*;
 
 import io.reactivex.functions.*;
-import io.reactivex.internal.functions.Functions;
+import io.reactivex.internal.functions.*;
 import io.reactivex.internal.subscribers.*;
 import io.reactivex.internal.util.*;
 
@@ -103,6 +103,9 @@ public static <T> void subscribe(Publisher<? extends T> o) {
      */
     public static <T> void subscribe(Publisher<? extends T> o, final Consumer<? super T> onNext,
             final Consumer<? super Throwable> onError, final Action onComplete) {
+        ObjectHelper.requireNonNull(onNext, "onNext is null");
+        ObjectHelper.requireNonNull(onError, "onError is null");
+        ObjectHelper.requireNonNull(onComplete, "onComplete is null");
         subscribe(o, new LambdaSubscriber<T>(onNext, onError, onComplete, Functions.REQUEST_MAX));
     }
 }
diff --git a/src/main/java/io/reactivex/internal/operators/observable/ObservableBlockingSubscribe.java b/src/main/java/io/reactivex/internal/operators/observable/ObservableBlockingSubscribe.java
index 8ddd579099..1151c280fc 100644
--- a/src/main/java/io/reactivex/internal/operators/observable/ObservableBlockingSubscribe.java
+++ b/src/main/java/io/reactivex/internal/operators/observable/ObservableBlockingSubscribe.java
@@ -17,7 +17,7 @@
 
 import io.reactivex.*;
 import io.reactivex.functions.*;
-import io.reactivex.internal.functions.Functions;
+import io.reactivex.internal.functions.*;
 import io.reactivex.internal.observers.*;
 import io.reactivex.internal.util.*;
 
@@ -97,6 +97,9 @@ public static <T> void subscribe(ObservableSource<? extends T> o) {
      */
     public static <T> void subscribe(ObservableSource<? extends T> o, final Consumer<? super T> onNext,
             final Consumer<? super Throwable> onError, final Action onComplete) {
+        ObjectHelper.requireNonNull(onNext, "onNext is null");
+        ObjectHelper.requireNonNull(onError, "onError is null");
+        ObjectHelper.requireNonNull(onComplete, "onComplete is null");
         subscribe(o, new LambdaObserver<T>(onNext, onError, onComplete, Functions.emptyConsumer()));
     }
 }
diff --git a/src/main/java/io/reactivex/subscribers/TestSubscriber.java b/src/main/java/io/reactivex/subscribers/TestSubscriber.java
index 0a90beb500..e16af8feaf 100644
--- a/src/main/java/io/reactivex/subscribers/TestSubscriber.java
+++ b/src/main/java/io/reactivex/subscribers/TestSubscriber.java
@@ -118,6 +118,9 @@ public TestSubscriber(Subscriber<? super T> actual) {
      */
     public TestSubscriber(Subscriber<? super T> actual, long initialRequest) {
         super();
+        if (initialRequest < 0) {
+            throw new IllegalArgumentException("Negative initial request not allowed");
+        }
         this.actual = actual;
         this.subscription = new AtomicReference<Subscription>();
         this.missedRequested = new AtomicLong(initialRequest);
diff --git a/src/test/java/io/reactivex/ParamValidationCheckerTest.java b/src/test/java/io/reactivex/ParamValidationCheckerTest.java
new file mode 100644
index 0000000000..3a69a87565
--- /dev/null
+++ b/src/test/java/io/reactivex/ParamValidationCheckerTest.java
@@ -0,0 +1,1117 @@
+/**
+ * Copyright (c) 2016-present, RxJava Contributors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in
+ * compliance with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the License is
+ * distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See
+ * the License for the specific language governing permissions and limitations under the License.
+ */
+
+package io.reactivex;
+
+import java.lang.reflect.*;
+import java.util.*;
+import java.util.concurrent.*;
+
+import org.junit.Test;
+import org.reactivestreams.*;
+
+import io.reactivex.disposables.Disposable;
+import io.reactivex.exceptions.TestException;
+import io.reactivex.functions.*;
+import io.reactivex.internal.functions.Functions;
+import io.reactivex.plugins.RxJavaPlugins;
+import io.reactivex.schedulers.Schedulers;
+
+/**
+ * Check that static and instance methods validate their parameters against
+ * null and invalid values properly.
+ */
+public class ParamValidationCheckerTest {
+
+    @Test(timeout = 30000)
+    public void checkFlowable() {
+        checkClass(Flowable.class);
+    }
+
+    @Test(timeout = 30000)
+    public void checkObservable() {
+        checkClass(Observable.class);
+    }
+
+    @Test(timeout = 30000)
+    public void checkSingle() {
+        checkClass(Single.class);
+    }
+
+    @Test(timeout = 30000)
+    public void checkMaybe() {
+        checkClass(Maybe.class);
+    }
+
+    @Test(timeout = 30000)
+    public void checkCompletable() {
+        checkClass(Completable.class);
+    }
+
+    // ---------------------------------------------------------------------------------------
+    // ---------------------------------------------------------------------------------------
+
+    static Map<String, List<ParamOverride>> overrides;
+
+    static Map<String, List<ParamIgnore>> ignores;
+
+    static Map<Class<?>, Object> defaultValues;
+
+    static Map<Class<?>, List<Object>> defaultInstances;
+
+    static {
+        overrides = new HashMap<String, List<ParamOverride>>();
+
+        // ***********************************************************************************************************************
+
+        // zero index allowed
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.NON_NEGATIVE, "elementAt", Long.TYPE));
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.NON_NEGATIVE, "elementAt", Long.TYPE, Object.class));
+
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.NON_NEGATIVE, "elementAtOrError", Long.TYPE));
+
+        // negative skip count is ignored
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "skip", Long.TYPE));
+        // negative skip time is considered as zero skip time
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "skip", Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "skip", Long.TYPE, TimeUnit.class, Scheduler.class));
+
+        // can start with zero initial request
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.NON_NEGATIVE, "test", Long.TYPE));
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.NON_NEGATIVE, "test", Long.TYPE, Boolean.TYPE));
+
+        // negative timeout time is considered as zero timeout time
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "timeout", Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "timeout", Long.TYPE, TimeUnit.class, Scheduler.class));
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "timeout", Long.TYPE, TimeUnit.class, Publisher.class));
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "timeout", Long.TYPE, TimeUnit.class, Scheduler.class, Publisher.class));
+
+        // negative buffer time is considered as zero buffer time
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "buffer", Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "buffer", Long.TYPE, TimeUnit.class, Integer.TYPE));
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "buffer", Long.TYPE, TimeUnit.class, Scheduler.class));
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "buffer", Long.TYPE, TimeUnit.class, Scheduler.class, Integer.TYPE));
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "buffer", Long.TYPE, TimeUnit.class, Scheduler.class, Integer.TYPE, Callable.class, Boolean.TYPE));
+
+        // negative time/skip is considered zero time/skip
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "buffer", Long.TYPE, Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "buffer", Long.TYPE, Long.TYPE, TimeUnit.class, Scheduler.class));
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "buffer", Long.TYPE, Long.TYPE, TimeUnit.class, Scheduler.class, Callable.class));
+        addOverride(new ParamOverride(Flowable.class, 1, ParamMode.ANY, "buffer", Long.TYPE, Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Flowable.class, 1, ParamMode.ANY, "buffer", Long.TYPE, Long.TYPE, TimeUnit.class, Scheduler.class));
+        addOverride(new ParamOverride(Flowable.class, 1, ParamMode.ANY, "buffer", Long.TYPE, Long.TYPE, TimeUnit.class, Scheduler.class, Callable.class));
+
+        // negative timeout is allowed
+        addOverride(new ParamOverride(Flowable.class, 1, ParamMode.ANY, "fromFuture", Future.class, Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Flowable.class, 1, ParamMode.ANY, "fromFuture", Future.class, Long.TYPE, TimeUnit.class, Scheduler.class));
+
+        // null default is allowed
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "blockingLast", Object.class));
+
+        // negative time is considered as zero time
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "timer", Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "timer", Long.TYPE, TimeUnit.class, Scheduler.class));
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "interval", Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "interval", Long.TYPE, TimeUnit.class, Scheduler.class));
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "interval", Long.TYPE, Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "interval", Long.TYPE, Long.TYPE, TimeUnit.class, Scheduler.class));
+        addOverride(new ParamOverride(Flowable.class, 1, ParamMode.ANY, "interval", Long.TYPE, Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Flowable.class, 1, ParamMode.ANY, "interval", Long.TYPE, Long.TYPE, TimeUnit.class, Scheduler.class));
+
+        // negative time is considered as zero time
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "delay", Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "delay", Long.TYPE, TimeUnit.class, Boolean.TYPE));
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "delay", Long.TYPE, TimeUnit.class, Scheduler.class));
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "delay", Long.TYPE, TimeUnit.class, Scheduler.class, Boolean.TYPE));
+
+        // null default is allowed
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "blockingMostRecent", Object.class));
+
+        // negative time is considered as zero time
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "delaySubscription", Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "delaySubscription", Long.TYPE, TimeUnit.class, Scheduler.class));
+
+        // null default is allowed
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "blockingFirst", Object.class));
+
+        // negative time is considered as zero time
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "debounce", Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "debounce", Long.TYPE, TimeUnit.class, Scheduler.class));
+
+        // null Action allowed
+        addOverride(new ParamOverride(Flowable.class, 1, ParamMode.ANY, "onBackpressureBuffer", Long.TYPE, Action.class, BackpressureOverflowStrategy.class));
+
+        // zero repeat is allowed
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.NON_NEGATIVE, "repeat", Long.TYPE));
+
+        // negative time is considered as zero time
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "replay", Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "replay", Long.TYPE, TimeUnit.class, Scheduler.class));
+        addOverride(new ParamOverride(Flowable.class, 1, ParamMode.ANY, "replay", Integer.TYPE, Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Flowable.class, 1, ParamMode.ANY, "replay", Integer.TYPE, Long.TYPE, TimeUnit.class, Scheduler.class));
+        addOverride(new ParamOverride(Flowable.class, 1, ParamMode.ANY, "replay", Function.class, Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Flowable.class, 1, ParamMode.ANY, "replay", Function.class, Long.TYPE, TimeUnit.class, Scheduler.class));
+        addOverride(new ParamOverride(Flowable.class, 2, ParamMode.ANY, "replay", Function.class, Integer.TYPE, Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Flowable.class, 2, ParamMode.ANY, "replay", Function.class, Integer.TYPE, Long.TYPE, TimeUnit.class, Scheduler.class));
+
+        // zero retry is allowed
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.NON_NEGATIVE, "retry", Long.TYPE));
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.NON_NEGATIVE, "retry", Long.TYPE, Predicate.class));
+
+        // negative time is considered as zero time
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "throttleWithTimeout", Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "throttleWithTimeout", Long.TYPE, TimeUnit.class, Scheduler.class));
+
+        // negative time is considered as zero time
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "take", Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "take", Long.TYPE, TimeUnit.class, Scheduler.class));
+
+        // zero retry is allowed
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.NON_NEGATIVE, "take", Long.TYPE));
+
+        // negative time is considered as zero time
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "sample", Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "sample", Long.TYPE, TimeUnit.class, Boolean.TYPE));
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "sample", Long.TYPE, TimeUnit.class, Scheduler.class));
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "sample", Long.TYPE, TimeUnit.class, Scheduler.class, Boolean.TYPE));
+
+        // negative time is considered as zero time
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "takeLast", Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "takeLast", Long.TYPE, TimeUnit.class, Boolean.TYPE));
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "takeLast", Long.TYPE, TimeUnit.class, Scheduler.class));
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "takeLast", Long.TYPE, TimeUnit.class, Scheduler.class, Boolean.TYPE));
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "takeLast", Long.TYPE, TimeUnit.class, Scheduler.class, Boolean.TYPE, Integer.TYPE));
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.NON_NEGATIVE, "takeLast", Long.TYPE, Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.NON_NEGATIVE, "takeLast", Long.TYPE, Long.TYPE, TimeUnit.class, Scheduler.class));
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.NON_NEGATIVE, "takeLast", Long.TYPE, Long.TYPE, TimeUnit.class, Scheduler.class, Boolean.TYPE, Integer.TYPE));
+        addOverride(new ParamOverride(Flowable.class, 1, ParamMode.ANY, "takeLast", Long.TYPE, Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Flowable.class, 1, ParamMode.ANY, "takeLast", Long.TYPE, Long.TYPE, TimeUnit.class, Scheduler.class));
+        addOverride(new ParamOverride(Flowable.class, 1, ParamMode.ANY, "takeLast", Long.TYPE, Long.TYPE, TimeUnit.class, Scheduler.class, Boolean.TYPE, Integer.TYPE));
+
+        // take last 0 is allowed
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.NON_NEGATIVE, "takeLast", Integer.TYPE));
+
+        // skip last 0 is allowed
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.NON_NEGATIVE, "skipLast", Integer.TYPE));
+
+        // negative time is considered as zero time
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "skipLast", Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "skipLast", Long.TYPE, TimeUnit.class, Boolean.TYPE));
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "skipLast", Long.TYPE, TimeUnit.class, Scheduler.class));
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "skipLast", Long.TYPE, TimeUnit.class, Scheduler.class, Boolean.TYPE));
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "skipLast", Long.TYPE, TimeUnit.class, Scheduler.class, Boolean.TYPE, Integer.TYPE));
+
+        // negative time is considered as zero time
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "throttleFirst", Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "throttleFirst", Long.TYPE, TimeUnit.class, Scheduler.class));
+
+        // negative time is considered as zero time
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "throttleLast", Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "throttleLast", Long.TYPE, TimeUnit.class, Scheduler.class));
+
+
+        // negative buffer time is considered as zero buffer time
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "window", Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "window", Long.TYPE, TimeUnit.class, Long.TYPE));
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "window", Long.TYPE, TimeUnit.class, Long.TYPE, Boolean.TYPE));
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "window", Long.TYPE, TimeUnit.class, Scheduler.class, Long.TYPE));
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "window", Long.TYPE, TimeUnit.class, Scheduler.class));
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "window", Long.TYPE, TimeUnit.class, Scheduler.class, Long.TYPE, Boolean.TYPE));
+        addOverride(new ParamOverride(Flowable.class, 0, ParamMode.ANY, "window", Long.TYPE, TimeUnit.class, Scheduler.class, Long.TYPE, Boolean.TYPE, Integer.TYPE));
+
+        // ***********************************************************************************************************************
+
+        // negative timeout time is considered as zero timeout time
+        addOverride(new ParamOverride(Completable.class, 0, ParamMode.ANY, "timeout", Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Completable.class, 0, ParamMode.ANY, "timeout", Long.TYPE, TimeUnit.class, Scheduler.class));
+        addOverride(new ParamOverride(Completable.class, 0, ParamMode.ANY, "timeout", Long.TYPE, TimeUnit.class, CompletableSource.class));
+        addOverride(new ParamOverride(Completable.class, 0, ParamMode.ANY, "timeout", Long.TYPE, TimeUnit.class, Scheduler.class, CompletableSource.class));
+
+        // negative time is considered as zero time
+        addOverride(new ParamOverride(Completable.class, 0, ParamMode.ANY, "timer", Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Completable.class, 0, ParamMode.ANY, "timer", Long.TYPE, TimeUnit.class, Scheduler.class));
+
+        // negative time is considered as zero time
+        addOverride(new ParamOverride(Completable.class, 0, ParamMode.ANY, "delay", Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Completable.class, 0, ParamMode.ANY, "delay", Long.TYPE, TimeUnit.class, Scheduler.class));
+        addOverride(new ParamOverride(Completable.class, 0, ParamMode.ANY, "delay", Long.TYPE, TimeUnit.class, Scheduler.class, Boolean.TYPE));
+
+        // zero repeat is allowed
+        addOverride(new ParamOverride(Completable.class, 0, ParamMode.NON_NEGATIVE, "repeat", Long.TYPE));
+
+        // zero retry is allowed
+        addOverride(new ParamOverride(Completable.class, 0, ParamMode.NON_NEGATIVE, "retry", Long.TYPE));
+
+        // negative time is considered as zero time
+        addOverride(new ParamOverride(Completable.class, 0, ParamMode.ANY, "blockingGet", Long.TYPE, TimeUnit.class));
+
+        // negative time is considered as zero time
+        addOverride(new ParamOverride(Completable.class, 0, ParamMode.ANY, "blockingAwait", Long.TYPE, TimeUnit.class));
+
+        // ***********************************************************************************************************************
+
+        // negative timeout time is considered as zero timeout time
+        addOverride(new ParamOverride(Maybe.class, 0, ParamMode.ANY, "timeout", Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Maybe.class, 0, ParamMode.ANY, "timeout", Long.TYPE, TimeUnit.class, Scheduler.class));
+        addOverride(new ParamOverride(Maybe.class, 0, ParamMode.ANY, "timeout", Long.TYPE, TimeUnit.class, MaybeSource.class));
+        addOverride(new ParamOverride(Maybe.class, 0, ParamMode.ANY, "timeout", Long.TYPE, TimeUnit.class, Scheduler.class, MaybeSource.class));
+
+        // negative time is considered as zero time
+        addOverride(new ParamOverride(Maybe.class, 0, ParamMode.ANY, "timer", Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Maybe.class, 0, ParamMode.ANY, "timer", Long.TYPE, TimeUnit.class, Scheduler.class));
+
+        // negative timeout is allowed
+        addOverride(new ParamOverride(Maybe.class, 1, ParamMode.ANY, "fromFuture", Future.class, Long.TYPE, TimeUnit.class));
+
+        // negative time is considered as zero time
+        addOverride(new ParamOverride(Maybe.class, 0, ParamMode.ANY, "delay", Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Maybe.class, 0, ParamMode.ANY, "delay", Long.TYPE, TimeUnit.class, Scheduler.class));
+
+        // zero repeat is allowed
+        addOverride(new ParamOverride(Maybe.class, 0, ParamMode.NON_NEGATIVE, "repeat", Long.TYPE));
+
+        // zero retry is allowed
+        addOverride(new ParamOverride(Maybe.class, 0, ParamMode.NON_NEGATIVE, "retry", Long.TYPE));
+        addOverride(new ParamOverride(Maybe.class, 0, ParamMode.NON_NEGATIVE, "retry", Long.TYPE, Predicate.class));
+
+        // negative time is considered as zero time
+        addOverride(new ParamOverride(Maybe.class, 0, ParamMode.ANY, "delaySubscription", Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Maybe.class, 0, ParamMode.ANY, "delaySubscription", Long.TYPE, TimeUnit.class, Scheduler.class));
+
+        // ***********************************************************************************************************************
+
+        // negative timeout time is considered as zero timeout time
+        addOverride(new ParamOverride(Single.class, 0, ParamMode.ANY, "timeout", Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Single.class, 0, ParamMode.ANY, "timeout", Long.TYPE, TimeUnit.class, Scheduler.class));
+        addOverride(new ParamOverride(Single.class, 0, ParamMode.ANY, "timeout", Long.TYPE, TimeUnit.class, SingleSource.class));
+        addOverride(new ParamOverride(Single.class, 0, ParamMode.ANY, "timeout", Long.TYPE, TimeUnit.class, Scheduler.class, SingleSource.class));
+
+        // negative time is considered as zero time
+        addOverride(new ParamOverride(Single.class, 0, ParamMode.ANY, "timer", Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Single.class, 0, ParamMode.ANY, "timer", Long.TYPE, TimeUnit.class, Scheduler.class));
+
+        // negative timeout is allowed
+        addOverride(new ParamOverride(Single.class, 1, ParamMode.ANY, "fromFuture", Future.class, Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Single.class, 1, ParamMode.ANY, "fromFuture", Future.class, Long.TYPE, TimeUnit.class, Scheduler.class));
+
+        // negative time is considered as zero time
+        addOverride(new ParamOverride(Single.class, 0, ParamMode.ANY, "delay", Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Single.class, 0, ParamMode.ANY, "delay", Long.TYPE, TimeUnit.class, Scheduler.class));
+
+
+        // zero repeat is allowed
+        addOverride(new ParamOverride(Single.class, 0, ParamMode.NON_NEGATIVE, "repeat", Long.TYPE));
+
+        // zero retry is allowed
+        addOverride(new ParamOverride(Single.class, 0, ParamMode.NON_NEGATIVE, "retry", Long.TYPE));
+
+        // negative time is considered as zero time
+        addOverride(new ParamOverride(Single.class, 0, ParamMode.ANY, "delaySubscription", Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Single.class, 0, ParamMode.ANY, "delaySubscription", Long.TYPE, TimeUnit.class, Scheduler.class));
+
+        // ***********************************************************************************************************************
+
+        // zero index allowed
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.NON_NEGATIVE, "elementAt", Long.TYPE));
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.NON_NEGATIVE, "elementAt", Long.TYPE, Object.class));
+
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.NON_NEGATIVE, "elementAtOrError", Long.TYPE));
+
+        // negative skip count is ignored
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "skip", Long.TYPE));
+        // negative skip time is considered as zero skip time
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "skip", Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "skip", Long.TYPE, TimeUnit.class, Scheduler.class));
+
+        // negative timeout time is considered as zero timeout time
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "timeout", Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "timeout", Long.TYPE, TimeUnit.class, Scheduler.class));
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "timeout", Long.TYPE, TimeUnit.class, ObservableSource.class));
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "timeout", Long.TYPE, TimeUnit.class, Scheduler.class, ObservableSource.class));
+
+        // negative buffer time is considered as zero buffer time
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "buffer", Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "buffer", Long.TYPE, TimeUnit.class, Integer.TYPE));
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "buffer", Long.TYPE, TimeUnit.class, Scheduler.class));
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "buffer", Long.TYPE, TimeUnit.class, Scheduler.class, Integer.TYPE));
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "buffer", Long.TYPE, TimeUnit.class, Scheduler.class, Integer.TYPE, Callable.class, Boolean.TYPE));
+
+        // negative time/skip is considered zero time/skip
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "buffer", Long.TYPE, Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "buffer", Long.TYPE, Long.TYPE, TimeUnit.class, Scheduler.class));
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "buffer", Long.TYPE, Long.TYPE, TimeUnit.class, Scheduler.class, Callable.class));
+        addOverride(new ParamOverride(Observable.class, 1, ParamMode.ANY, "buffer", Long.TYPE, Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Observable.class, 1, ParamMode.ANY, "buffer", Long.TYPE, Long.TYPE, TimeUnit.class, Scheduler.class));
+        addOverride(new ParamOverride(Observable.class, 1, ParamMode.ANY, "buffer", Long.TYPE, Long.TYPE, TimeUnit.class, Scheduler.class, Callable.class));
+
+        // negative timeout is allowed
+        addOverride(new ParamOverride(Observable.class, 1, ParamMode.ANY, "fromFuture", Future.class, Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Observable.class, 1, ParamMode.ANY, "fromFuture", Future.class, Long.TYPE, TimeUnit.class, Scheduler.class));
+
+        // null default is allowed
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "blockingLast", Object.class));
+
+        // negative time is considered as zero time
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "timer", Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "timer", Long.TYPE, TimeUnit.class, Scheduler.class));
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "interval", Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "interval", Long.TYPE, TimeUnit.class, Scheduler.class));
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "interval", Long.TYPE, Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "interval", Long.TYPE, Long.TYPE, TimeUnit.class, Scheduler.class));
+        addOverride(new ParamOverride(Observable.class, 1, ParamMode.ANY, "interval", Long.TYPE, Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Observable.class, 1, ParamMode.ANY, "interval", Long.TYPE, Long.TYPE, TimeUnit.class, Scheduler.class));
+
+        // negative time is considered as zero time
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "delay", Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "delay", Long.TYPE, TimeUnit.class, Boolean.TYPE));
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "delay", Long.TYPE, TimeUnit.class, Scheduler.class));
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "delay", Long.TYPE, TimeUnit.class, Scheduler.class, Boolean.TYPE));
+
+        // null default is allowed
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "blockingMostRecent", Object.class));
+
+        // negative time is considered as zero time
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "delaySubscription", Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "delaySubscription", Long.TYPE, TimeUnit.class, Scheduler.class));
+
+        // null default is allowed
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "blockingFirst", Object.class));
+
+        // negative time is considered as zero time
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "debounce", Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "debounce", Long.TYPE, TimeUnit.class, Scheduler.class));
+
+        // zero repeat is allowed
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.NON_NEGATIVE, "repeat", Long.TYPE));
+
+        // negative time is considered as zero time
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "replay", Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "replay", Long.TYPE, TimeUnit.class, Scheduler.class));
+        addOverride(new ParamOverride(Observable.class, 1, ParamMode.ANY, "replay", Integer.TYPE, Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Observable.class, 1, ParamMode.ANY, "replay", Integer.TYPE, Long.TYPE, TimeUnit.class, Scheduler.class));
+        addOverride(new ParamOverride(Observable.class, 1, ParamMode.ANY, "replay", Function.class, Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Observable.class, 1, ParamMode.ANY, "replay", Function.class, Long.TYPE, TimeUnit.class, Scheduler.class));
+        addOverride(new ParamOverride(Observable.class, 2, ParamMode.ANY, "replay", Function.class, Integer.TYPE, Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Observable.class, 2, ParamMode.ANY, "replay", Function.class, Integer.TYPE, Long.TYPE, TimeUnit.class, Scheduler.class));
+
+        // zero retry is allowed
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.NON_NEGATIVE, "retry", Long.TYPE));
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.NON_NEGATIVE, "retry", Long.TYPE, Predicate.class));
+
+        // negative time is considered as zero time
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "throttleWithTimeout", Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "throttleWithTimeout", Long.TYPE, TimeUnit.class, Scheduler.class));
+
+        // negative time is considered as zero time
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "take", Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "take", Long.TYPE, TimeUnit.class, Scheduler.class));
+
+        // zero retry is allowed
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.NON_NEGATIVE, "take", Long.TYPE));
+
+        // negative time is considered as zero time
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "sample", Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "sample", Long.TYPE, TimeUnit.class, Boolean.TYPE));
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "sample", Long.TYPE, TimeUnit.class, Scheduler.class));
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "sample", Long.TYPE, TimeUnit.class, Scheduler.class, Boolean.TYPE));
+
+        // negative time is considered as zero time
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "takeLast", Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "takeLast", Long.TYPE, TimeUnit.class, Boolean.TYPE));
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "takeLast", Long.TYPE, TimeUnit.class, Scheduler.class));
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "takeLast", Long.TYPE, TimeUnit.class, Scheduler.class, Boolean.TYPE));
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "takeLast", Long.TYPE, TimeUnit.class, Scheduler.class, Boolean.TYPE, Integer.TYPE));
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.NON_NEGATIVE, "takeLast", Long.TYPE, Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.NON_NEGATIVE, "takeLast", Long.TYPE, Long.TYPE, TimeUnit.class, Scheduler.class));
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.NON_NEGATIVE, "takeLast", Long.TYPE, Long.TYPE, TimeUnit.class, Scheduler.class, Boolean.TYPE, Integer.TYPE));
+        addOverride(new ParamOverride(Observable.class, 1, ParamMode.ANY, "takeLast", Long.TYPE, Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Observable.class, 1, ParamMode.ANY, "takeLast", Long.TYPE, Long.TYPE, TimeUnit.class, Scheduler.class));
+        addOverride(new ParamOverride(Observable.class, 1, ParamMode.ANY, "takeLast", Long.TYPE, Long.TYPE, TimeUnit.class, Scheduler.class, Boolean.TYPE, Integer.TYPE));
+
+        // take last 0 is allowed
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.NON_NEGATIVE, "takeLast", Integer.TYPE));
+
+        // skip last 0 is allowed
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.NON_NEGATIVE, "skipLast", Integer.TYPE));
+
+        // negative time is considered as zero time
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "skipLast", Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "skipLast", Long.TYPE, TimeUnit.class, Boolean.TYPE));
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "skipLast", Long.TYPE, TimeUnit.class, Scheduler.class));
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "skipLast", Long.TYPE, TimeUnit.class, Scheduler.class, Boolean.TYPE));
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "skipLast", Long.TYPE, TimeUnit.class, Scheduler.class, Boolean.TYPE, Integer.TYPE));
+
+        // negative time is considered as zero time
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "throttleFirst", Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "throttleFirst", Long.TYPE, TimeUnit.class, Scheduler.class));
+
+        // negative time is considered as zero time
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "throttleLast", Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "throttleLast", Long.TYPE, TimeUnit.class, Scheduler.class));
+
+
+        // negative buffer time is considered as zero buffer time
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "window", Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "window", Long.TYPE, TimeUnit.class, Long.TYPE));
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "window", Long.TYPE, TimeUnit.class, Long.TYPE, Boolean.TYPE));
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "window", Long.TYPE, TimeUnit.class, Scheduler.class, Long.TYPE));
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "window", Long.TYPE, TimeUnit.class, Scheduler.class));
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "window", Long.TYPE, TimeUnit.class, Scheduler.class, Long.TYPE, Boolean.TYPE));
+        addOverride(new ParamOverride(Observable.class, 0, ParamMode.ANY, "window", Long.TYPE, TimeUnit.class, Scheduler.class, Long.TYPE, Boolean.TYPE, Integer.TYPE));
+
+        // -----------------------------------------------------------------------------------
+
+        ignores = new HashMap<String, List<ParamIgnore>>();
+
+        // needs special param validation due to (long)start + end - 1 <= Integer.MAX_VALUE
+        addIgnore(new ParamIgnore(Flowable.class, "range", Integer.TYPE, Integer.TYPE));
+        addIgnore(new ParamIgnore(Flowable.class, "rangeLong", Long.TYPE, Long.TYPE));
+        addIgnore(new ParamIgnore(Flowable.class, "intervalRange", Long.TYPE, Long.TYPE, Long.TYPE, TimeUnit.class));
+        addIgnore(new ParamIgnore(Flowable.class, "intervalRange", Long.TYPE, Long.TYPE, Long.TYPE, Long.TYPE, TimeUnit.class));
+        addIgnore(new ParamIgnore(Flowable.class, "intervalRange", Long.TYPE, Long.TYPE, Long.TYPE, TimeUnit.class, Scheduler.class));
+        addIgnore(new ParamIgnore(Flowable.class, "intervalRange", Long.TYPE, Long.TYPE, Long.TYPE, Long.TYPE, TimeUnit.class, Scheduler.class));
+
+        addIgnore(new ParamIgnore(Flowable.class, "unsafeCreate", Publisher.class));
+
+        // needs special param validation due to (long)start + end - 1 <= Integer.MAX_VALUE
+        addIgnore(new ParamIgnore(Observable.class, "range", Integer.TYPE, Integer.TYPE));
+        addIgnore(new ParamIgnore(Observable.class, "rangeLong", Long.TYPE, Long.TYPE));
+        addIgnore(new ParamIgnore(Observable.class, "intervalRange", Long.TYPE, Long.TYPE, Long.TYPE, TimeUnit.class));
+        addIgnore(new ParamIgnore(Observable.class, "intervalRange", Long.TYPE, Long.TYPE, Long.TYPE, Long.TYPE, TimeUnit.class));
+        addIgnore(new ParamIgnore(Observable.class, "intervalRange", Long.TYPE, Long.TYPE, Long.TYPE, TimeUnit.class, Scheduler.class));
+        addIgnore(new ParamIgnore(Observable.class, "intervalRange", Long.TYPE, Long.TYPE, Long.TYPE, Long.TYPE, TimeUnit.class, Scheduler.class));
+
+        addIgnore(new ParamIgnore(Observable.class, "unsafeCreate", ObservableSource.class));
+
+        addIgnore(new ParamIgnore(Maybe.class, "unsafeCreate", MaybeSource.class));
+
+        addIgnore(new ParamIgnore(Single.class, "unsafeCreate", SingleSource.class));
+
+        addIgnore(new ParamIgnore(Completable.class, "unsafeCreate", CompletableSource.class));
+
+        // -----------------------------------------------------------------------------------
+
+        defaultValues = new HashMap<Class<?>, Object>();
+
+        defaultValues.put(Publisher.class, new NeverPublisher());
+        defaultValues.put(Flowable.class, new NeverPublisher());
+
+        defaultValues.put(ObservableSource.class, new NeverObservable());
+        defaultValues.put(Observable.class, new NeverObservable());
+
+        defaultValues.put(SingleSource.class, new NeverSingle());
+        defaultValues.put(Single.class, new NeverSingle());
+
+        defaultValues.put(MaybeSource.class, new NeverMaybe());
+        defaultValues.put(Maybe.class, new NeverMaybe());
+
+        defaultValues.put(CompletableSource.class, new NeverCompletable());
+        defaultValues.put(Completable.class, new NeverCompletable());
+
+        defaultValues.put(Action.class, Functions.EMPTY_ACTION);
+        defaultValues.put(Runnable.class, Functions.EMPTY_RUNNABLE);
+        defaultValues.put(Consumer.class, Functions.emptyConsumer());
+        defaultValues.put(LongConsumer.class, Functions.EMPTY_LONG_CONSUMER);
+        defaultValues.put(Function.class, Functions.justFunction(1));
+        defaultValues.put(Callable.class, Functions.justCallable(1));
+        defaultValues.put(Iterable.class, Collections.emptyList());
+        defaultValues.put(Object.class, 1);
+        defaultValues.put(Class.class, Integer.class);
+        Object af = new AllFunctionals();
+        for (Class<?> interfaces : AllFunctionals.class.getInterfaces()) {
+            defaultValues.put(interfaces, af);
+        }
+        defaultValues.put(TimeUnit.class, TimeUnit.SECONDS);
+        defaultValues.put(Scheduler.class, Schedulers.single());
+        defaultValues.put(BackpressureStrategy.class, BackpressureStrategy.MISSING);
+        defaultValues.put(BackpressureOverflowStrategy.class, BackpressureOverflowStrategy.ERROR);
+        defaultValues.put(Throwable.class, new TestException());
+
+        defaultValues.put(Publisher[].class, new Publisher[] { new NeverPublisher(), new NeverPublisher() });
+        defaultValues.put(ObservableSource[].class, new ObservableSource[] { new NeverObservable(), new NeverObservable() });
+        defaultValues.put(SingleSource[].class, new SingleSource[] { new NeverSingle(), new NeverSingle() });
+        defaultValues.put(MaybeSource[].class, new MaybeSource[] { new NeverMaybe(), new NeverMaybe() });
+        defaultValues.put(CompletableSource[].class, new CompletableSource[] { new NeverCompletable(), new NeverCompletable() });
+
+        defaultValues.put(Object[].class, new Object[] { new Object(), new Object() });
+        defaultValues.put(Future.class, new FutureTask<Object>(Functions.EMPTY_RUNNABLE, 1));
+
+        // -----------------------------------------------------------------------------------
+
+        defaultInstances = new HashMap<Class<?>, List<Object>>();
+
+//        addDefaultInstance(Flowable.class, Flowable.empty(), "Empty()");
+//        addDefaultInstance(Flowable.class, Flowable.empty().hide(), "Empty().Hide()");
+        addDefaultInstance(Flowable.class, Flowable.just(1), "Just(1)");
+        addDefaultInstance(Flowable.class, Flowable.just(1).hide(), "Just(1).Hide()");
+//        addDefaultInstance(Flowable.class, Flowable.range(1, 3), "Range(1, 3)");
+//        addDefaultInstance(Flowable.class, Flowable.range(1, 3).hide(), "Range(1, 3).Hide()");
+
+//        addDefaultInstance(Observable.class, Observable.empty(), "Empty()");
+//        addDefaultInstance(Observable.class, Observable.empty().hide(), "Empty().Hide()");
+        addDefaultInstance(Observable.class, Observable.just(1), "Just(1)");
+        addDefaultInstance(Observable.class, Observable.just(1).hide(), "Just(1).Hide()");
+//        addDefaultInstance(Observable.class, Observable.range(1, 3), "Range(1, 3)");
+//        addDefaultInstance(Observable.class, Observable.range(1, 3).hide(), "Range(1, 3).Hide()");
+
+        addDefaultInstance(Completable.class, Completable.complete(), "Complete()");
+        addDefaultInstance(Completable.class, Completable.complete().hide(), "Complete().hide()");
+
+        addDefaultInstance(Single.class, Single.just(1), "Just(1)");
+        addDefaultInstance(Single.class, Single.just(1).hide(), "Just(1).Hide()");
+
+        addDefaultInstance(Maybe.class, Maybe.just(1), "Just(1)");
+        addDefaultInstance(Maybe.class, Maybe.just(1).hide(), "Just(1).Hide()");
+    }
+
+    static void addIgnore(ParamIgnore ignore) {
+        String key = ignore.toString();
+        List<ParamIgnore> list = ignores.get(key);
+        if (list == null) {
+            list = new ArrayList<ParamIgnore>();
+            ignores.put(key, list);
+        }
+        list.add(ignore);
+    }
+
+    static void addOverride(ParamOverride ignore) {
+        String key = ignore.toString();
+        List<ParamOverride> list = overrides.get(key);
+        if (list == null) {
+            list = new ArrayList<ParamOverride>();
+            overrides.put(key, list);
+        }
+        list.add(ignore);
+    }
+
+    static void addDefaultInstance(Class<?> clazz, Object o, String tag) {
+        List<Object> list = defaultInstances.get(clazz);
+        if (list == null) {
+            list = new ArrayList<Object>();
+            defaultInstances.put(clazz, list);
+        }
+        list.add(o);
+        list.add(tag);
+    }
+
+    Object defaultPrimitive(Class<?> clazz, ParamOverride override) {
+        if (Integer.TYPE == clazz) {
+            if (override != null) {
+                return 0;
+            }
+            return 1;
+        }
+
+        if (Long.TYPE == clazz) {
+            if (override != null) {
+                return 0L;
+            }
+            return 1L;
+        }
+
+        if (Boolean.TYPE == clazz) {
+            return true;
+        }
+
+        return null;
+    }
+
+    void addCheckPrimitive(Class<?> clazz, ParamOverride override, List<Object> values) {
+        if (Integer.TYPE == clazz) {
+            values.add(-2);
+            values.add(override != null && override.mode == ParamMode.ANY);
+            values.add(-1);
+            values.add(override != null && override.mode == ParamMode.ANY);
+            values.add(0);
+            values.add(override != null);
+            values.add(1);
+            values.add(true); // should succeed
+            values.add(2);
+            values.add(true);
+        }
+
+        if (Long.TYPE == clazz) {
+            values.add(-2L);
+            values.add(override != null && override.mode == ParamMode.ANY);
+            values.add(-1L);
+            values.add(override != null && override.mode == ParamMode.ANY);
+            values.add(0L);
+            values.add(override != null);
+            values.add(1L);
+            values.add(true); // should succeed
+            values.add(2L);
+            values.add(true);
+        }
+
+        if (Boolean.TYPE == clazz) {
+            values.add(false);
+            values.add(true);
+            values.add(true);
+            values.add(true);
+        }
+    }
+
+    void checkClass(Class<?> clazz) {
+        List<Throwable> errors = TestHelper.trackPluginErrors();
+        try {
+            StringBuilder b = new StringBuilder();
+            int fail = 0;
+
+            outer:
+            for (Method m : clazz.getMethods()) {
+                if (m.getDeclaringClass() != clazz) {
+                    continue;
+                }
+
+                String key = clazz.getName() + " " + m.getName();
+
+                List<ParamIgnore> ignoreList = ignores.get(key);
+                if (ignoreList != null) {
+                    for (ParamIgnore e : ignoreList) {
+                        if (Arrays.equals(e.arguments, m.getParameterTypes())) {
+                            System.out.println("CheckClass - ignore: " + m);
+                            continue outer;
+                        }
+                    }
+                }
+
+                List<ParamOverride> overrideList = overrides.get(key);
+
+                List<Object> baseObjects = new ArrayList<Object>();
+
+                if ((m.getModifiers() & Modifier.STATIC) != 0) {
+                    baseObjects.add(null);
+                    baseObjects.add("NULL");
+                } else {
+                    List<Object> defaultInstancesList = defaultInstances.get(clazz);
+                    if (defaultInstancesList == null) {
+                        b.append("\r\nNo default instances for " + clazz);
+                        fail++;
+                        continue outer;
+                    }
+                    baseObjects.addAll(defaultInstancesList);
+                }
+
+                for (int ii = 0; ii < baseObjects.size(); ii += 2) {
+                    Object baseObject = baseObjects.get(ii);
+                    Object tag = baseObjects.get(ii + 1);
+                    Class<?>[] params = m.getParameterTypes();
+                    int n = params.length;
+
+                    for (int i = 0; i < n; i++) {
+                        ParamOverride overrideEntry = null;
+                        if (overrideList != null) {
+                            for (ParamOverride e : overrideList) {
+                                if (e.index == i && Arrays.equals(e.arguments, params)) {
+                                    overrideEntry = e;
+                                    break;
+                                }
+                            }
+                        }
+
+                        Class<?> entryClass = params[i];
+
+                        Object[] callParams = new Object[n];
+
+                        for (int j = 0; j < n; j++) {
+                            if (j != i) {
+                                if (params[j].isPrimitive()) {
+                                    ParamOverride overrideParam = null;
+                                    if (overrideList != null) {
+                                        for (ParamOverride e : overrideList) {
+                                            if (e.index == j && Arrays.equals(e.arguments, params)) {
+                                                overrideParam = e;
+                                                break;
+                                            }
+                                        }
+                                    }
+                                    Object def = defaultPrimitive(params[j], overrideParam);
+                                    if (def == null) {
+                                        b.append("\r\nMissing default non-null value for " + m + " # " + j + " (" + params[j] + ")");
+                                        fail++;
+                                        continue outer;
+                                    }
+                                    callParams[j] = def;
+                                } else {
+                                    Object def = defaultValues.get(params[j]);
+                                    if (def == null) {
+                                        b.append("\r\nMissing default non-null value for " + m + " # " + j + " (" + params[j] + ")");
+                                        fail++;
+                                        continue outer;
+                                    }
+                                    callParams[j] = def;
+                                }
+                            }
+                        }
+
+                        List<Object> entryValues = new ArrayList<Object>();
+
+                        if (entryClass.isPrimitive()) {
+                            addCheckPrimitive(params[i], overrideEntry, entryValues);
+                        } else {
+                            entryValues.add(null);
+                            entryValues.add(overrideEntry != null && overrideEntry.mode == ParamMode.ANY);
+
+                            Object def = defaultValues.get(params[i]);
+                            if (def == null) {
+                                b.append("\r\nMissing default non-null value for " + m + " # " + i + " (" + params[i] + ")");
+                                fail++;
+                                continue outer;
+                            }
+                            entryValues.add(def);
+                            entryValues.add(true);
+                        }
+
+                        for (int k = 0; k < entryValues.size(); k += 2) {
+                            Object[] callParams2 = callParams.clone();
+
+                            Object p = entryValues.get(k);
+                            callParams2[i] = p;
+                            boolean shouldSucceed = (Boolean)entryValues.get(k + 1);
+
+                            boolean success = false;
+                            Throwable error = null;
+                            errors.clear();
+                            try {
+                                m.invoke(baseObject, callParams2);
+                                success = true;
+                            } catch (Throwable ex) {
+                                // let it fail
+                                error = ex;
+                            }
+
+                            if (success != shouldSucceed) {
+                                fail++;
+                                if (shouldSucceed) {
+                                    b.append("\r\nFailed (should have succeeded): " + m + " # " + i + " = " + p + ", tag = " + tag + ", params = " + Arrays.toString(callParams2));
+                                    b.append("\r\n    ").append(error);
+                                    if (error.getCause() != null) {
+                                        b.append("\r\n    ").append(error.getCause());
+                                    }
+                                } else {
+                                    b.append("\r\nNo failure (should have failed): " + m + " # " + i + " = " + p + ", tag = " + tag + ", params = " + Arrays.toString(callParams2));
+                                }
+                                continue outer;
+                            }
+                            if (!errors.isEmpty()) {
+                                fail++;
+                                b.append("\r\nUndeliverable errors:");
+                                for (Throwable err : errors) {
+                                    b.append("\r\n    ").append(err);
+                                    if (err.getCause() != null) {
+                                        b.append("\r\n    ").append(err.getCause());
+                                    }
+                                }
+                                continue outer;
+                            }
+                        }
+                    }
+                }
+            }
+
+            if (fail != 0) {
+                throw new AssertionError("Parameter validation problems: " + fail + b.toString());
+            }
+        } finally {
+            RxJavaPlugins.reset();
+        }
+    }
+
+    @SuppressWarnings("rawtypes")
+    static final class AllFunctionals
+    implements BiFunction, BiConsumer,
+    Predicate, BiPredicate, BooleanSupplier,
+    Function3, Function4, Function5, Function6, Function7, Function8, Function9,
+    FlowableOnSubscribe, ObservableOnSubscribe, SingleOnSubscribe, MaybeOnSubscribe, CompletableOnSubscribe,
+    FlowableTransformer, ObservableTransformer, SingleTransformer, MaybeTransformer, CompletableTransformer,
+    Subscriber, FlowableSubscriber, Observer, SingleObserver, MaybeObserver, CompletableObserver,
+    FlowableOperator, ObservableOperator, SingleOperator, MaybeOperator, CompletableOperator,
+    Comparator
+    {
+
+        @Override
+        public Object apply(Object t1, Object t2, Object t3, Object t4, Object t5, Object t6, Object t7, Object t8,
+                Object t9) throws Exception {
+            return null;
+        }
+
+        @Override
+        public Object apply(Object t1, Object t2, Object t3, Object t4, Object t5, Object t6, Object t7, Object t8)
+                throws Exception {
+            return null;
+        }
+
+        @Override
+        public Object apply(Object t1, Object t2, Object t3, Object t4, Object t5, Object t6, Object t7)
+                throws Exception {
+            return null;
+        }
+
+        @Override
+        public Object apply(Object t1, Object t2, Object t3, Object t4, Object t5, Object t6) throws Exception {
+            return null;
+        }
+
+        @Override
+        public Object apply(Object t1, Object t2, Object t3, Object t4, Object t5) throws Exception {
+            return null;
+        }
+
+        @Override
+        public Object apply(Object t1, Object t2, Object t3, Object t4) throws Exception {
+            return null;
+        }
+
+        @Override
+        public Object apply(Object t1, Object t2, Object t3) throws Exception {
+            return null;
+        }
+
+        @Override
+        public void accept(Object t1, Object t2) throws Exception {
+        }
+
+        @Override
+        public Object apply(Object t1, Object t2) throws Exception {
+            return null;
+        }
+
+        @Override
+        public void subscribe(CompletableEmitter e) throws Exception {
+        }
+
+        @Override
+        public void subscribe(MaybeEmitter e) throws Exception {
+        }
+
+        @Override
+        public void subscribe(SingleEmitter e) throws Exception {
+        }
+
+        @Override
+        public void subscribe(ObservableEmitter e) throws Exception {
+        }
+
+        @Override
+        public void subscribe(FlowableEmitter e) throws Exception {
+        }
+
+        @Override
+        public boolean test(Object t1, Object t2) throws Exception {
+            return false;
+        }
+
+        @Override
+        public boolean test(Object t) throws Exception {
+            return false;
+        }
+
+        @Override
+        public void onSuccess(Object t) {
+        }
+
+        @Override
+        public void onSubscribe(Disposable d) {
+        }
+
+        @Override
+        public void onSubscribe(Subscription s) {
+            s.request(Long.MAX_VALUE);
+        }
+
+        @Override
+        public void onNext(Object t) {
+        }
+
+        @Override
+        public void onError(Throwable t) {
+        }
+
+        @Override
+        public void onComplete() {
+        }
+
+        @Override
+        public CompletableSource apply(Completable upstream) {
+            return upstream;
+        }
+
+        @Override
+        public MaybeSource apply(Maybe upstream) {
+            return upstream;
+        }
+
+        @Override
+        public SingleSource apply(Single upstream) {
+            return upstream;
+        }
+
+        @Override
+        public ObservableSource apply(Observable upstream) {
+            return upstream;
+        }
+
+        @Override
+        public Publisher apply(Flowable upstream) {
+            return upstream;
+        }
+
+        @Override
+        public CompletableObserver apply(CompletableObserver observer) throws Exception {
+            return observer;
+        }
+
+        @Override
+        public MaybeObserver apply(MaybeObserver observer) throws Exception {
+            return observer;
+        }
+
+        @Override
+        public SingleObserver apply(SingleObserver observer) throws Exception {
+            return observer;
+        }
+
+        @Override
+        public Observer apply(Observer observer) throws Exception {
+            return observer;
+        }
+
+        @Override
+        public Subscriber apply(Subscriber observer) throws Exception {
+            return observer;
+        }
+
+        @Override
+        public boolean getAsBoolean() throws Exception {
+            return false;
+        }
+
+        @Override
+        public int compare(Object o1, Object o2) {
+            return 0;
+        }
+    }
+
+    enum ParamMode {
+        ANY,
+        NON_NEGATIVE
+    }
+
+    static final class ParamIgnore {
+        final Class<?> clazz;
+        final String name;
+        final Class<?>[] arguments;
+
+        ParamIgnore(Class<?> clazz, String name, Class<?>... arguments) {
+            this.clazz = clazz;
+            this.name = name;
+            this.arguments = arguments;
+        }
+
+        @Override
+        public String toString() {
+            return clazz.getName() + " " + name;
+        }
+    }
+
+    static final class ParamOverride {
+        final Class<?> clazz;
+        final int index;
+        final ParamMode mode;
+        final String name;
+        final Class<?>[] arguments;
+
+        ParamOverride(Class<?> clazz, int index, ParamMode mode, String name, Class<?>... arguments) {
+            this.clazz = clazz;
+            this.index = index;
+            this.mode = mode;
+            this.name = name;
+            this.arguments = arguments;
+
+            try {
+                clazz.getMethod(name, arguments);
+            } catch (Exception ex) {
+                throw new AssertionError(ex);
+            }
+        }
+
+        @Override
+        public String toString() {
+            return clazz.getName() + " " + name;
+        }
+    }
+
+    static final class NeverPublisher extends Flowable<Object> {
+
+        @Override
+        public void subscribeActual(Subscriber<? super Object> s) {
+            // not invoked, the class is a placeholder default value
+        }
+
+        @Override
+        public String toString() {
+            return "NeverFlowable";
+        }
+    }
+
+    static final class NeverObservable extends Observable<Object> {
+
+        @Override
+        public void subscribeActual(Observer<? super Object> s) {
+            // not invoked, the class is a placeholder default value
+        }
+
+        @Override
+        public String toString() {
+            return "NeverFlowable";
+        }
+    }
+
+    static final class NeverSingle extends Single<Object> {
+
+        @Override
+        public void subscribeActual(SingleObserver<? super Object> s) {
+            // not invoked, the class is a placeholder default value
+        }
+
+        @Override
+        public String toString() {
+            return "NeverSingle";
+        }
+    }
+
+    static final class NeverMaybe extends Maybe<Object> {
+
+        @Override
+        public void subscribeActual(MaybeObserver<? super Object> s) {
+            // not invoked, the class is a placeholder default value
+        }
+
+        @Override
+        public String toString() {
+            return "NeverMaybe";
+        }
+    }
+    static final class NeverCompletable extends Completable {
+
+        @Override
+        public void subscribeActual(CompletableObserver s) {
+            // not invoked, the class is a placeholder default value
+        }
+
+        @Override
+        public String toString() {
+            return "NeverCompletable";
+        }
+    }
+}
diff --git a/src/test/java/io/reactivex/observable/ObservableNullTests.java b/src/test/java/io/reactivex/observable/ObservableNullTests.java
index e79eee87ff..c39205f8bc 100644
--- a/src/test/java/io/reactivex/observable/ObservableNullTests.java
+++ b/src/test/java/io/reactivex/observable/ObservableNullTests.java
@@ -2427,8 +2427,8 @@ public void toSortedListNull() {
         just1.toSortedList(null);
     }
 
-    @Test
-    public void toMapKeyNullAllowed() {
+    @Test(expected = NullPointerException.class)
+    public void toMapKeyNull() {
         just1.toMap(null);
     }