Flutter Twilio Conversation chat title body are null when send text

I am implementing Twilio Conversations chat in Flutter. I have configured notification in Android according to document. Register token for notification. There is one issue that when I tried to listen for messages from the notification event I am getting data from the message event but getting null object for title and body. Does anyone have idea about it?

Please refer code I am trying to implement.

FirebaseMessaging.onMessage.listen(_onMessage);

 void _onMessage(RemoteMessage event) {
    Log.debug('_onMessage -> ${event.notification?.title} -> ${event.notification?.body}');
    Log.debug('_onMessage -> ${event.data}');
    Log.debug('_onMessage -> ${event.messageType}');
  }