private function setModifiedSince(Request $request, Item $item)
    {
        if ($modifiedAt = $item->getCreation()) {
            $modifiedAt->setTimezone(new DateTimeZone('GMT'));

            $date = sprintf('%s GMT', $modifiedAt->format('l, d-M-y H:i:s'));

            $request->addHeader('If-Modified-Since', $date);
        }
    }