public function setThumbnail(string $imageContents) : void
    {
        $parameters = [
            [
                'name' => 'threadThumbnail',
                'contents' => $imageContents,
                'headers' => [
                    'Content-Type' => 'image/jpeg',
                    'Content-Transfer-Encoding' => 'binary',
                ]
            ]
        ];

        $this->putMultiPart(sprintf(MessageThread::MESSAGE_THREAD_ENDPOINT . 'threads/%s/thumbnail', $this->messageThreadId), $parameters);
    }