diff --git a/src/xitdb/hash_map.clj b/src/xitdb/hash_map.clj
index df01503..8be3add 100644
--- a/src/xitdb/hash_map.clj
+++ b/src/xitdb/hash_map.clj
@@ -56,7 +56,7 @@
          (= (into {} this) (into {} other))))
 
   clojure.lang.Seqable
-  (seq [this]
+  (seq [_]
     (map-seq rhm))
 
   clojure.lang.IFn
@@ -161,7 +161,7 @@
         (common/-read-from-cursor (conversion/map-write-cursor whm key)))))
 
   clojure.lang.Seqable
-  (seq [this]
+  (seq [_]
     (map-seq whm))
 
   clojure.core.protocols/IKVReduce
@@ -192,6 +192,3 @@
 
 (defn xhash-map-counted [^ReadCursor read-cursor]
   (->XITDBHashMap (ReadCountedHashMap. read-cursor)))
-
-
-
diff --git a/src/xitdb/hash_set.clj b/src/xitdb/hash_set.clj
index 6d2da8b..ff1110d 100644
--- a/src/xitdb/hash_set.clj
+++ b/src/xitdb/hash_set.clj
@@ -41,7 +41,7 @@
     (operations/set-item-count rhs))
 
   clojure.lang.Seqable
-  (seq [_]
+  (seq [this]
     (set-seq rhs))
 
   clojure.lang.ILookup
@@ -117,7 +117,7 @@
     (operations/set-item-count whs))
 
   clojure.lang.Seqable
-  (seq [_]
+  (seq [this]
     (set-seq whs))
 
   clojure.lang.ILookup
diff --git a/src/xitdb/util/operations.clj b/src/xitdb/util/operations.clj
index 410bf78..848c858 100644
--- a/src/xitdb/util/operations.clj
+++ b/src/xitdb/util/operations.clj
@@ -197,31 +197,33 @@
 ;; ============================================================================
 
 (defn map-seq
-  "Return a lazy seq of key-value MapEntry pairs."
+  "Return a lazy seq of key-value MapEntry pairs, or nil if empty."
   [^ReadHashMap rhm read-from-cursor]
   (let [it (.iterator rhm)]
-    (letfn [(step []
-              (lazy-seq
-                (when (.hasNext it)
-                  (let [cursor (.next it)
-                        kv     (.readKeyValuePair cursor)
-                        k      (read-from-cursor (.-keyCursor kv))]
-                    (let [v (read-from-cursor (.-valueCursor kv))]
-                      (cons (clojure.lang.MapEntry. k v) (step)))))))]
-      (step))))
+    (when (.hasNext it)
+      (letfn [(step []
+                (lazy-seq
+                  (when (.hasNext it)
+                    (let [cursor (.next it)
+                          kv     (.readKeyValuePair cursor)
+                          k      (read-from-cursor (.-keyCursor kv))]
+                      (let [v (read-from-cursor (.-valueCursor kv))]
+                        (cons (clojure.lang.MapEntry. k v) (step)))))))]
+        (step)))))
 
 (defn set-seq
-  "Return a lazy seq values from the set."
+  "Return a lazy seq values from the set, or nil if empty."
   [rhm read-from-cursor]
   (let [it (.iterator rhm)]
-    (letfn [(step []
-              (lazy-seq
-                (when (.hasNext it)
-                  (let [cursor (.next it)
-                        kv     (.readKeyValuePair cursor)
-                        v      (read-from-cursor (.-keyCursor kv))]
-                    (cons v (step))))))]
-      (step))))
+    (when (.hasNext it)
+      (letfn [(step []
+                (lazy-seq
+                  (when (.hasNext it)
+                    (let [cursor (.next it)
+                          kv     (.readKeyValuePair cursor)
+                          v      (read-from-cursor (.-keyCursor kv))]
+                      (cons v (step))))))]
+        (step)))))
 
 (defn array-seq
   "Creates a lazy sequence from a ReadArrayList.
diff --git a/test/xitdb/map_test.clj b/test/xitdb/map_test.clj
index 976690f..c7276e5 100644
--- a/test/xitdb/map_test.clj
+++ b/test/xitdb/map_test.clj
@@ -1,6 +1,7 @@
 (ns xitdb.map-test
   (:require
     [clojure.test :refer :all]
+    [xitdb.db :as xdb]
     [xitdb.test-utils :as tu :refer [with-db]]))
 
 (deftest map-with-complex-keys
@@ -19,4 +20,16 @@
       (swap! db update :foo dissoc [2 :baz])
       
       (is (= {:foo {[1 :bar] 31}}
-             (tu/materialize @db))))))
\ No newline at end of file
+             (tu/materialize @db))))))
+
+(deftest KeysTest
+  (with-open [db (xdb/xit-db :memory)]
+    (reset! db {})
+    (is (= nil (keys @db)))
+    (is (= 0 (count (keys @db))))))
+
+(deftest KeysTestSet
+  (with-open [db (xdb/xit-db :memory)]
+    (reset! db #{})
+    (is (= 0 (count (keys @db))))
+    (is (= nil (keys @db)))))