title: How to handle FirebaseInstanceId.getInstance().getToken() = null
body: <p>I have just migrated to FCM. I have added my class that extends from FirebaseInstanceIdService to receive a refreshedToken as and when appropriate.</p>
  
  <p>My question is specific to the case when user installs my app first time and due to some reason, unable to receive a registration Id from onTokenRefresh. How are we supposed to handle this? Can I set a broadcast receiver from my FirebaseInstanceIdService class which will notify the Main activity when a registration Id is received?</p>