1.x: fix merge/flatMap crashing on an inner scalar of null

src/main/java/rx/internal/operators/OperatorMerge.java

@@ -475,7 +475,7 @@ protected void queueScalar(T value) {
                 }
                 this.queue = q;
             }
-            if (!q.offer(value)) {
+            if (!q.offer(nl.next(value))) {
                 unsubscribe();
                 onError(OnErrorThrowable.addValueAsLastCause(new MissingBackpressureException(), value));
                 return;

src/test/java/rx/internal/operators/OperatorMergeTest.java

@@ -28,10 +28,10 @@
 import org.mockito.*;
 
 import rx.*;
-import rx.Observable.OnSubscribe;
-import rx.Scheduler.Worker;
 import rx.Observable;
+import rx.Observable.OnSubscribe;
 import rx.Observer;
+import rx.Scheduler.Worker;
 import rx.functions.*;
 import rx.internal.util.RxRingBuffer;
 import rx.observers.TestSubscriber;
@@ -1353,4 +1353,21 @@ public void zeroMaxConcurrent() {
             assertEquals("maxConcurrent > 0 required but it was 0", e.getMessage());
         }
     }
+
+    @Test
+    public void mergeJustNull() {
+        TestSubscriber<Integer> ts = new TestSubscriber<Integer>(0);
+
+        Observable.range(1, 2).flatMap(new Func1<Integer, Observable<Integer>>() {
+            @Override
+            public Observable<Integer> call(Integer t) {
+                return Observable.just(null);
+            }
+        }).subscribe(ts);
+
+        ts.requestMore(2);
+        ts.assertValues(null, null);
+        ts.assertNoErrors();
+        ts.assertCompleted();
+    }
 }