public static function normalizeConfig($config, $key, $plural = null)
    {
        if (null === $plural) {
            $plural = $key.'s';
        }

        if (isset($config[$plural])) {
            return $config[$plural];
        }

        if (isset($config[$key])) {
            if (is_string($config[$key]) || !is_int(key($config[$key]))) {
                // only one
                return  array($config[$key]);
            }

            return  $config[$key];
        }

        return array();
    }