public function getChecksumAlgorithm() : ?string
    {
        $checksumHeader = $this->getRequest()->header('Upload-Checksum');

        if (empty($checksumHeader)) {
            return self::DEFAULT_CHECKSUM_ALGORITHM;
        }

        list($checksumAlgorithm, /* $checksum */) = explode(' ', $checksumHeader);

        return $checksumAlgorithm;
    }