[Java] Add null ref test for websocket

clients/java/signalr/src/main/java/com/microsoft/signalr/WebSocketTransport.java

@@ -89,7 +89,7 @@ class WebSocketTransport implements Transport {
     void onClose(Integer code, String reason) {
         logger.info("WebSocket connection stopping with " +
                 "code {} and reason '{}'.", code, reason);
-        if (code != 1000) {
+        if (code == null || code != 1000) {
             onClose.invoke(reason);
         }
         else {

clients/java/signalr/src/test/java/com/microsoft/signalr/WebSocketTransportTest.java

@@ -6,10 +6,15 @@ package com.microsoft.signalr;
 import static org.junit.jupiter.api.Assertions.*;
 
 import java.util.HashMap;
+import java.util.Map;
 import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicBoolean;
 
 import org.junit.jupiter.api.Test;
 
+import io.reactivex.Completable;
+import io.reactivex.Single;
+
 class WebSocketTransportTest {
     @Test
     public void WebsocketThrowsIfItCantConnect() {
@@ -17,4 +22,59 @@ class WebSocketTransportTest {
         RuntimeException exception = assertThrows(RuntimeException.class, () -> transport.start("http://www.example.com").blockingAwait(1, TimeUnit.SECONDS));
         assertEquals("There was an error starting the Websockets transport.", exception.getMessage());
     }
+
+    @Test
+    public void CanPassNullExitCodeToOnClosed() {
+        WebSocketTransport transport = new WebSocketTransport(new HashMap<>(), new WebSocketTestHttpClient());
+        AtomicBoolean closed = new AtomicBoolean();
+        transport.setOnClose(reason -> {
+            closed.set(true);
+        });
+        transport.start("");
+        transport.stop();
+        assertTrue(closed.get());
+    }
+
+    class WebSocketTestHttpClient extends HttpClient {
+        @Override
+        public Single<HttpResponse> send(HttpRequest request) {
+            return null;
+        }
+
+        @Override
+        public WebSocketWrapper createWebSocket(String url, Map<String, String> headers) {
+            return new TestWrapper();
+        }
+    }
+
+    class TestWrapper extends WebSocketWrapper {
+        private WebSocketOnClosedCallback onClose;
+
+        @Override
+        public Completable start() {
+            return Completable.complete();
+        }
+
+        @Override
+        public Completable stop() {
+            if (onClose != null) {
+                onClose.invoke(null, "");
+            }
+            return Completable.complete();
+        }
+
+        @Override
+        public Completable send(String message) {
+            return null;
+        }
+
+        @Override
+        public void setOnReceive(OnReceiveCallBack onReceive) {
+        }
+
+        @Override
+        public void setOnClose(WebSocketOnClosedCallback onClose) {
+            this.onClose = onClose;
+        }
+    }
 }