public function getSupportedPrivilegeSet(INode $node, array &$supportedPrivilegeSet)
    {
        if ($node instanceof ICalendar) {
            $supportedPrivilegeSet['{DAV:}read']['aggregates']['{'.self::NS_CALDAV.'}read-free-busy'] = [
                'abstract' => false,
                'aggregates' => [],
            ];
        }
    }