public function setAsNotModified()
    {
        $this->setStatusCode(304);
        $this->setContent('');

        // remove headers that MUST NOT be included with 304 Not Modified responses
        $headersToRemove = [
            'Allow',
            'Content-Encoding',
            'Content-Language',
            'Content-Length',
            'Content-MD5',
            'Content-Type',
            'Last-Modified'
        ];
        foreach ($headersToRemove as $header) {
            $this->headers->removeKey($header);
        }

        return $this;
    }