title: android onActivityResult: Attempt to invoke virtual method on a null object reference
body: <p>im developing plugin for cordova android. it open up a custom activity and return sets of data back to the plugin.</p>
  
  <p>all things are running well on the activity. but when the activity finished, it crashed and give me this error:</p>
  
  <pre><code>Attempt to invoke virtual method 'void org.apache.cordova.CallbackContext.success(java.lang.String)' on a null object reference
  E/AndroidRuntime( 2697):    at android.app.ActivityThread.deliverResults(ActivityThread.java:3539)
  E/AndroidRuntime( 2697):    at android.app.ActivityThread.handleSendResult(ActivityThread.java:3582)
  E/AndroidRuntime( 2697):    at android.app.ActivityThread.access$1300(ActivityThread.java:144)
  E/AndroidRuntime( 2697):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1327)
  E/AndroidRuntime( 2697):    at android.os.Handler.dispatchMessage(Handler.java:102)
  E/AndroidRuntime( 2697):    at android.os.Looper.loop(Looper.java:135)
  E/AndroidRuntime( 2697):    at android.app.ActivityThread.main(ActivityThread.java:5221)
  E/AndroidRuntime( 2697):    at java.lang.reflect.Method.invoke(Native Method)
  E/AndroidRuntime( 2697):    at java.lang.reflect.Method.invoke(Method.java:372)
  E/AndroidRuntime( 2697):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
  E/AndroidRuntime( 2697):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
  E/AndroidRuntime( 2697): Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void org.apache.cordova.CallbackContext.success(java.lang.String)' on a null object reference
  E/AndroidRuntime( 2697):    at com.faiz.faizOk.onActivityResult(faizOk.java:147)
  E/AndroidRuntime( 2697):    at org.apache.cordova.CordovaInterfaceImpl.onActivityResult(CordovaInterfaceImpl.java:151)
  E/AndroidRuntime( 2697):    at org.apache.cordova.CordovaActivity.onActivityResult(CordovaActivity.java:348)
  E/AndroidRuntime( 2697):    at android.app.Activity.dispatchActivityResult(Activity.java:6139)
  E/AndroidRuntime( 2697):    at android.app.ActivityThread.deliverResults(ActivityThread.java:3535)
  E/AndroidRuntime( 2697):    
  ... 10 more
  </code></pre>
  
  <p>this is my android <code>onActivityResult</code> method</p>
  
  <pre><code>@Override
  public void onActivityResult(int requestCode, int resultCode, Intent data) {
      System.out.println("finished native activity proceess...");
  
      String message = " :finished activity from native: ";
      callbackContext.success(message);
  }
  </code></pre>