@rafaelfranca Because the docs said so :p

> If you don't need the confirmation validation, just don't set any value to the password_confirmation attribute and the validation will not be triggered.

This allows you to have the option to require the password confirmation or not – if you have a password confirmation input, the form will send that field and you'll get an empty string, and this validation fires; if you don't that, don't include the input in the form, and it'll be `nil`, and the validation won't fire.

This is not the right implementation though. When this behaviour was originally documented, it was handled by the  `validates_confirmation_of` rule (because the rule only fires when the confirmation is not nil).