App crashes when pressing play button

[yohannes-taye]

E/AndroidRuntime: FATAL EXCEPTION: main Process: com.example.user.ettalocation, PID: 20427 java.lang.NullPointerException: Attempt to invoke virtual method 'void com.example.user.ettalocation.LocationService.stopLogging()' on a null object reference at com.example.user.ettalocation.MainActivity$5.onClick(MainActivity.java:187) at android.view.View.performClick(View.java:5265) at android.view.View$PerformClick.run(View.java:21534) at android.os.Handler.handleCallback(Handler.java:815) at android.os.Handler.dispatchMessage(Handler.java:104) at android.os.Looper.loop(Looper.java:207) at android.app.ActivityThread.main(ActivityThread.java:5728) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:789) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:679)