public function getXRequestId()
    {
        if (is_null($this->xRequestId)) {
            if (!empty($this->headers)) {
                foreach ($this->headers as $header) {
                    $position = strpos(strtolower($header), self::HEADER_PREFIX_X_REQUEST_ID);
                    if ($position === 0) {
                        $this->xRequestId = substr($header, strlen(self::HEADER_PREFIX_X_REQUEST_ID));
                        break;
                    }
                }
            }
        }

        return $this->xRequestId;
    }