protected function processKey($key) {
        if (is_string($key)) {
            return $key;
        } else {
            $keyStr = Json::encode($key);
            return md5($keyStr);
        }
    }
protected function processKey($key) {
        if (is_string($key)) {
            return $key;
        } else {
            $keyStr = Json::encode($key);
            return md5($keyStr);
        }
    }
protected function processKey ( $ key ) { if ( is_string ( $ key ) ) { return $ key ; } else { $ keyStr = Json :: encode ( $ key ) ; return md5 ( $ keyStr ) ; } }
Process key. Ensure that key is string
@param string|array $key
@return string
Process key . Ensure that key is string