private void checkNotNull(Object object, String message) {
    if (object == null) {
      throw new IllegalArgumentException(message);
    }
  }
Unregisters NetworkEvents.
It should be executed in onDestroy() method in activity
or during destroying instance of class extending Application.
network-events-library/src/main/java/com/github/pwittchen/networkevents/library/NetworkEvents.java