public function getFixity(): string {
        $uri     = $this->fedora->sanitizeUri($this->uri);
        $request = new Request('GET', $uri . '/fcr:fixity');
        $resp    = $this->fedora->sendRequest($request);

        $graph     = new Graph();
        $graph->parse($resp->getBody());
        $res       = $graph->resource($uri);
        $fixityRes = $graph->resource($res->getResource('http://www.loc.gov/premis/rdf/v1#hasFixity'));
        $fixity    = $fixityRes->getResource('http://www.loc.gov/premis/rdf/v1#hasMessageDigest');
        return $fixity->getUri();
    }