protected function createAsseticCollection($files = null, $content = null)
    {
        $assets = array();
        if ($files) {
            foreach ($files as $file) {
                $assets[] = new \Assetic\Asset\FileAsset($file);
            }
        }
        if ($content) {
            foreach ($content as $item) {
                $assets[] = new \Assetic\Asset\StringAsset($item);
            }
        }
        return new \Assetic\Asset\AssetCollection($assets);
    }