title: Rails: Validate only on create, or on update when field is not blank
body: <p>How can I restrict a Rails validation to check only on create OR when the field isn't blank? I'm creating a user settings page for an app I'm working on and the problem is that, when updating using the parameters provided by the form, the settings will only save when both a password and password confirmation are present. I would like these password fields to validate on create no matter what, but only on update when they are provided.</p>