Uncaught TypeError: Cannot read property '$login_field' of undefined

[xurde]

Just followed the steps in Readme and when I try to submit Sign Up, I get this error which interrupts runtime.
Any clue on how can I proceed?

Thanks in advance.

[xurde]

It's obviously related to this line of code:

login = model.send(:"_#{User.login_field}")

I can't see where this login_field method is declared or configured anywhere else.

[xurde]

I managed to solve this issue adding a class method to User model.

  def self.login_field
    'email'
  end

But I think this should be handled in the signup controller using the existing method use_username?