protected function getOsimages(Server $model = null)
    {
        if ($model !== null) {
            $type = $model->type;
        } else {
            $type = null;
        }

        $models = ServerHelper::getOsimages($type);

        if ($models === null) {
            throw new NotFoundHttpException('The requested page does not exist.');
        }

        return $models;
    }