'Add a registration request for the user.
:rtype : RegisterUser'

def add_register_user(self, username, first_name, last_name, email, password='', hashed_password=''):

    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
