public function notModified()
    {
        $this->_createStream();
        $this->_setStatus(304);

        $remove = [
            'Allow',
            'Content-Encoding',
            'Content-Language',
            'Content-Length',
            'Content-MD5',
            'Content-Type',
            'Last-Modified'
        ];
        foreach ($remove as $header) {
            $this->_clearHeader($header);
        }
    }