Add a registration request for the user.

            :rtype : RegisterUser

def add_register_user(
        self, username, first_name, last_name, email, password="", hashed_password=""
    ):
        """
            Add a registration request for the user.

            :rtype : RegisterUser
        """
        register_user = self.registeruser_model()
        register_user.username = username
        register_user.email = email
        register_user.first_name = first_name
        register_user.last_name = last_name
        if hashed_password:
            register_user.password = hashed_password
        else:
            register_user.password = generate_password_hash(password)
        register_user.registration_hash = str(uuid.uuid1())
        try:
            self.get_session.add(register_user)
            self.get_session.commit()
            return register_user
        except Exception as e:
            log.error(c.LOGMSG_ERR_SEC_ADD_REGISTER_USER.format(str(e)))
            self.appbuilder.get_session.rollback()
            return None