/**
* Sets the ETag
* @param string $eTag A unique identifier of the current version of
* the content
* @return null
*/
public function setETag($eTag = null)
{
if ($eTag === null) {
$this->headers->removeHeader(Header::HEADER_ETAG);
} else {
$this->headers->setHeader(Header::HEADER_ETAG, $eTag);
}
}
