public function getLoadedPage($default = null)
    {
        if (!$this->loadedPage) {
            if (is_callable($default)) {
                $page = call_user_func($default, $this);
                if ($page !== null) {
                    $this->setLoadedPage($page);
                }
            }

            if (!$this->loadedPage) {
                throw new NotFoundHttpException("There is no page currently loaded, but it was expected");
            }
        }
        return $this->loadedPage;
    }