Support for null in mapAsync and fromCompletionStage #25475

akka-stream-tests/src/test/java/akka/stream/javadsl/FlowTest.java

@@ -813,6 +813,21 @@ public class FlowTest extends StreamTest {
     probe.expectMsgEquals("C");
   }
 
+  @Test
+  public void mustBeAbleToUseMapAsyncForFutureWithNullResult() throws Exception {
+    final Iterable<Integer> input = Arrays.asList(1, 2, 3);
+    Flow<Integer, Void, NotUsed> flow =
+        Flow.of(Integer.class).mapAsync(1, x -> CompletableFuture.completedFuture(null));
+    List<Void> result =
+        Source.from(input)
+            .via(flow)
+            .runWith(Sink.seq(), materializer)
+            .toCompletableFuture()
+            .get(3, TimeUnit.SECONDS);
+
+    assertEquals(0, result.size());
+  }
+
   @Test
   public void mustBeAbleToUseCollectType() throws Exception {
     final TestKit probe = new TestKit(system);