fix nullref

Author: BrennanConroy

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

@@ -1394,12 +1394,10 @@ public void close() {
 
             if (pingTimer != null) {
                 pingTimer.cancel();
-                pingTimer = null;
             }
 
             if (this.handshakeTimeout != null) {
                 this.handshakeTimeout.shutdownNow();
-                this.handshakeTimeout = null;
             }
         }