src/Cache/ExtendedCache.php
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