public function propPatch($path, DAV\PropPatch $propPatch)
    {
        $propPatch->handle('{DAV:}group-member-set', function ($value) use ($path) {
            if (is_null($value)) {
                $memberSet = [];
            } elseif ($value instanceof Href) {
                $memberSet = array_map(
                    [$this->server, 'calculateUri'],
                    $value->getHrefs()
                );
            } else {
                throw new DAV\Exception('The group-member-set property MUST be an instance of Sabre\DAV\Property\HrefList or null');
            }
            $node = $this->server->tree->getNodeForPath($path);
            if (!($node instanceof IPrincipal)) {
                // Fail
                return false;
            }

            $node->setGroupMemberSet($memberSet);
            // We must also clear our cache, just in case

            $this->principalMembershipCache = [];

            return true;
        });
    }