public static function config($key, $config = null)
    {
        deprecationWarning(
            get_called_class() . '::config() is deprecated. ' .
            'Use setConfig()/getConfig() instead.'
        );

        if ($config !== null || is_array($key)) {
            static::setConfig($key, $config);

            return null;
        }

        return static::getConfig($key);
    }