public static function buildKey($key)
    {
        if (is_numeric($key)) {
            return $key;
        } elseif (is_string($key)) {
            return ctype_alnum($key) && StringHelper::byteLength($key) <= 32 ? $key : md5($key);
        } elseif (is_array($key)) {
            if (count($key) == 1) {
                return self::buildKey(reset($key));
            }
            ksort($key); // ensure order is always the same
            $isNumeric = true;
            foreach ($key as $k => $value) {
                if (!is_numeric($value)) {
                    $isNumeric = false;
                }
                $key[$k] = strval($value); // <-THIS
            }
            if ($isNumeric) {
                return implode('-', $key);
            }
        }

        return md5(json_encode($key));
    }