public function Subscriber_Update($user_id, $subscription_state, $division, $attributes, $allow_resubscribe = true,
                                      $append = false) {
        $data = $this->_package_subscriber_elements($subscription_state, $division, $attributes);

        if (is_null($allow_resubscribe) === false) {
            $data->allowResubscribe = $allow_resubscribe;
        }

        if (is_null($append) === false) {
            $data->append = $append;
        }

        $ret = $this->_call_api('put', "{$this->_url}/subscribers/$user_id", $data);

        return $ret;
    }