NPE on disconnect

[dbrgn]

11-02 16:22:22.246 31806-31806/org.saltyrtc.demo.app E/AndroidRuntime: FATAL EXCEPTION: main
                                                                       Process: org.saltyrtc.demo.app, PID: 31806
                                                                       java.lang.NullPointerException: Attempt to invoke virtual method 'com.neovisionaries.ws.client.WebSocket com.neovisionaries.ws.client.WebSocket.disconnect(int)' on a null object reference
                                                                           at org.saltyrtc.client.signaling.Signaling.disconnect(Signaling.java:215)
                                                                           at org.saltyrtc.client.signaling.Signaling.disconnect(Signaling.java:232)
                                                                           at org.saltyrtc.client.SaltyRTC.disconnect(SaltyRTC.java:135)
                                                                           at org.saltyrtc.demo.app.MainActivity.stop(MainActivity.java:253)
                                                                           at org.saltyrtc.demo.app.MainActivity$3$1.run(MainActivity.java:171)
                                                                           at android.os.Handler.handleCallback(Handler.java:739)
                                                                           at android.os.Handler.dispatchMessage(Handler.java:95)
                                                                           at android.os.Looper.loop(Looper.java:168)
                                                                           at android.app.ActivityThread.main(ActivityThread.java:5845)
                                                                           at java.lang.reflect.Method.invoke(Native Method)
                                                                           at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:797)
                                                                           at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:687)