This will prevent a notification from being seen by a user if its
subject is deleted or undergoes some kind of permission change (eg.
a discussion is moved into a private tag)
ref #1380
When loading notifications, $this->type was null and thus array_get
was returning an array instead of null. I assume this issue was
introduced in a Laravel version upgrade? Anyway, this fixes it.
I didn't think this change through and it's going to be too difficult
to implement right now. It can wait until we do the notifications
revamp. For now reverting back to the old structure, with the
`sender_id` column renamed to `from_user_id`.
They will probably be refactored away at a later stage (when we get
rid of the command bus). Until then, this lets us remove the
Flarum\Core namespace and actually feels quite clean.
