code: public void onDestroy(Activity activity) {
      if (sameActivity(activity)) {
        hideCurrentScreen();
        this.activity = null;
        container = null;
        menu = null;
      }
    }
docs: Notifies Navigator that the activity's onDestroy lifecycle callback has been hit. Call this method from
  {@link Activity#onDestroy() onDestroy} of the Activity associated with this Navigator.
  
  This method will hid the current screen, and clear references to this Navigators associated activity, menu, and
  container view, if the activity parameter is the same as the activity provided to this Navigator in
  {@link #onCreate(Activity, Bundle) onCreate}.
  
  @param activity  activity that received onDestroy callback