Spring Cloud Command Router implementation

Apparently a Spring RestController doesn't like it when you return null, hence we return "" instead when a dispatch without callback has succeeded.
Additionally change the 'receiveCommand(...)' method to return a CompletableFuture.completedFuture() in every if/else/catch block rather than creating a
CompletableFuture at the start of the function and calling 'complet(...)' on it

distributed-commandbus/src/main/java/org/axonframework/commandhandling/distributed/spring/SpringHttpCommandBusConnector.java

@@ -102,28 +102,26 @@ public Registration subscribe(String commandName, MessageHandler<? super Command
     public <C, R> CompletableFuture<?> receiveCommand(
             @RequestBody SpringHttpDispatchMessage<C> dispatchMessage) throws ExecutionException, InterruptedException {
         CommandMessage<C> commandMessage = dispatchMessage.getCommandMessage(serializer);
-        CompletableFuture<SpringHttpReplyMessage<R>> result = new CompletableFuture<>();
-
         if (dispatchMessage.isExpectReply()) {
             try {
                 SpringHttpReplyFutureCallback<C, R> replyFutureCallback = new SpringHttpReplyFutureCallback<>();
                 localCommandBus.dispatch(commandMessage, replyFutureCallback);
                 return replyFutureCallback;
             } catch (Exception e) {
                 LOGGER.error("Could not dispatch command", e);
-                result.complete(new SpringHttpReplyMessage<>(commandMessage.getIdentifier(), null, e, serializer));
+                return CompletableFuture.completedFuture(
+                        new SpringHttpReplyMessage<>(commandMessage.getIdentifier(), null, e, serializer));
             }
         } else {
             try {
                 localCommandBus.dispatch(commandMessage);
-                result.complete(null);
+                return CompletableFuture.completedFuture("");
             } catch (Exception e) {
                 LOGGER.error("Could not dispatch command", e);
-                result.complete(new SpringHttpReplyMessage<>(commandMessage.getIdentifier(), null, e, serializer));
+                return CompletableFuture.completedFuture(
+                        new SpringHttpReplyMessage<>(commandMessage.getIdentifier(), null, e, serializer));
             }
         }
-
-        return result;
     }
 
     public class SpringHttpReplyFutureCallback<C, R>  extends CompletableFuture<SpringHttpReplyMessage>

distributed-commandbus/src/test/java/org/axonframework/commandhandling/distributed/spring/SpringHttpCommandBusConnectorTest.java

@@ -250,10 +250,9 @@ public void testReceiveCommandHandlesCommandWithCallbackFails() throws Exception
 
     @Test
     public void testReceiveCommandHandlesCommandWithoutCallback() throws Exception {
-        SpringHttpReplyMessage result =
-                (SpringHttpReplyMessage) testSubject.receiveCommand(buildDispatchMessage(false)).get();
+        String result = (String) testSubject.receiveCommand(buildDispatchMessage(false)).get();
 
-        assertNull(result);
+        assertEquals("", result);
 
         verify(localCommandBus).dispatch(any());
     }