public function length($bytes = null)
    {
        deprecationWarning(
            'Response::length() is deprecated. ' .
            'Use withLength() instead.'
        );

        if ($bytes !== null) {
            $this->_setHeader('Content-Length', $bytes);
        }

        if ($this->hasHeader('Content-Length')) {
            return $this->getHeaderLine('Content-Length');
        }

        return null;
    }