public function Link($action = null)
    {
        // Check configured url_segment
        $url = $this->config()->get('url_segment');
        if ($url) {
            $link = Controller::join_links($url, $action, '/');

            // Give extensions the chance to modify by reference
            $this->extend('updateLink', $link, $action);
            return $link;
        }

        // no link defined by default
        trigger_error(
            'Request handler ' . static::class . ' does not have a url_segment defined. ' . 'Relying on this link may be an application error',
            E_USER_WARNING
        );
        return null;
    }