I have installed auth_signup module to ensure signup functionality, but when I am trying to signup a new user either public user or template user, I am getting an exception. By investing on this I found that in
auth_signup/res_users.py , exception is where the following line of code are:

try:
    with cr.savepoint():
        return self.copy(cr, uid, template_user_id, values, context=context)

 I don't why cr.savepoint is returning None