user without email address

My site is using drupal for facebook to create user accounts and today I was getting 'unable to send mail' errors when updating a node.
For a short time I did not require email addresses to create user account (with facebook connect) and it seems this was the problem as I had 1 user without a 'mail' entry in the 'users' table.
Maybe this module should check for a valid $to variable before calling drupal_mail on line 2945 ?

I then went and deleted the user but would still get the error.
The module does not remove the undelivered mail from the 'watcher_notify_queue' table.
Maybe this should be done in the '_watcher_db_delete_user_settings' function in 'watcher.db.inc' ?