static public function extract($data, $keys=null)
    {
        if ($data) {
            if ($keys) {
                $list = [];
                $keys = static::explode('\,\|', $keys);
                foreach ($keys as $k) {
                    $list[] = isset($data[$k]) ? $data[$k] : null;
                }
                return $list;
            }
        }
        return $data;
    }