hub.register(token, tag); throws exception if already registered

hub.register() crashes the second time (i.e. you cannot run this or change the registered tag every time on launch).
This used to work in a previous version, where we can re-register a new tag when a user logged out of their account and registered/signed in with a new one.

We are handling this by storing the FCM tokens, but this function should be failing gracefully, or calling a update registration with new tag instead. It shouldn't throw a random exception.

Thanks!