Allow sending null params in Java client (#11272)

src/SignalR/clients/java/signalr/src/main/java/com/microsoft/signalr/HubConnection.java

@@ -577,6 +577,10 @@ public class HubConnection {
     }
 
     Object[] checkUploadStream(Object[] args, List<String> streamIds) {
+        if (args == null) {
+            return new Object[] { null };
+        }
+
         List<Object> params = new ArrayList<>(Arrays.asList(args));
         for (Object arg: args) {
             if (arg instanceof Observable) {
@@ -587,7 +591,7 @@ public class HubConnection {
                 this.streamMap.put(streamId, stream);
             }
         }
-
+        
         return params.toArray();
     }
 

src/SignalR/clients/java/signalr/src/test/java/com/microsoft/signalr/HubConnectionTest.java

@@ -954,6 +954,42 @@ class HubConnectionTest {
 
         assertEquals(Integer.valueOf(42), result.timeout(1000, TimeUnit.MILLISECONDS).blockingGet());
     }
+    
+    @Test
+    public void canSendNullArgInInvocation() {
+        MockTransport mockTransport = new MockTransport();
+        HubConnection hubConnection = TestUtils.createHubConnection("http://example.com", mockTransport);
+
+        hubConnection.start().timeout(1, TimeUnit.SECONDS).blockingAwait();
+
+        AtomicBoolean done = new AtomicBoolean();
+        Single<String> result = hubConnection.invoke(String.class, "fixedMessage", null);
+        result.doOnSuccess(value -> done.set(true));
+        assertEquals("{\"type\":1,\"invocationId\":\"1\",\"target\":\"fixedMessage\",\"arguments\":[null]}" + RECORD_SEPARATOR, mockTransport.getSentMessages()[1]);
+        assertFalse(done.get());
+
+        mockTransport.receiveMessage("{\"type\":3,\"invocationId\":\"1\",\"result\":\"Hello World\"}" + RECORD_SEPARATOR);
+
+        assertEquals("Hello World", result.timeout(1000, TimeUnit.MILLISECONDS).blockingGet());
+    }
+
+    @Test
+    public void canSendMultipleNullArgsInInvocation() {
+        MockTransport mockTransport = new MockTransport();
+        HubConnection hubConnection = TestUtils.createHubConnection("http://example.com", mockTransport);
+
+        hubConnection.start().timeout(1, TimeUnit.SECONDS).blockingAwait();
+
+        AtomicBoolean done = new AtomicBoolean();
+        Single<String> result = hubConnection.invoke(String.class, "fixedMessage", null, null);
+        result.doOnSuccess(value -> done.set(true));
+        assertEquals("{\"type\":1,\"invocationId\":\"1\",\"target\":\"fixedMessage\",\"arguments\":[null,null]}"+ RECORD_SEPARATOR, mockTransport.getSentMessages()[1]);
+        assertFalse(done.get());
+
+        mockTransport.receiveMessage("{\"type\":3,\"invocationId\":\"1\",\"result\":\"Hello World\"}" + RECORD_SEPARATOR);
+
+        assertEquals("Hello World", result.timeout(1000, TimeUnit.MILLISECONDS).blockingGet());
+    }
 
     @Test
     public void multipleInvokesWaitForOwnCompletionMessage() {