public function file($key)
    {
        if (!isset($_FILES[$key])) {
            return null;
        }

        if (!is_array($_FILES[$key]['name'])) {
            return new UploadFile($_FILES[$key]);
        }

        $files = $_FILES[$key];

        $collect = [];

        foreach ($files['name'] as $key => $name) {
            $file['name'] = $name;

            $file['type'] = $files['type'][$key];

            $file['size'] = $files['size'][$key];

            $file['error'] = $files['error'][$key];

            $file['tmp_name'] = $files['tmp_name'][$key];

            $collect[] = new UploadFile($file);
        }

        return new Collection($collect);
    }