public function getFlash($key = null)
    {
        if (! is_null($key)) {
            $value = null;

            if ($this->hasFlash($key)) {
                $value = $this->get('_nur_flash')[$key];
                unset($_SESSION['_nur_flash'][$key]);
            }

            return $value;
        }

        return $key;
    }