Question: Allow user to sign up without username?

[sleepless]

I need a user to be able to sign up with only his e-mail address. The username is optional and can later be set in the user's profile. I managed to overwrite the validator so that's it's possible to sign up with e-mail only.

The issue I now have is that you can't sign up again with a different e-mail address if there already is an user whose username is null. I'm still getting the error that the credentials provided have already been used.

I do not post any username so the username is NULL. The problem is that confide is checking if there is already an user with username NULL. How can I avoid that without losing the functionality if I want a user to be able to login with username or e-mail later?