fix panic in userlog service

Signed-off-by: jkoberg <jkoberg@owncloud.com>

changelog/unreleased/fix-userlog-panic.md

@@ -0,0 +1,5 @@
+Bugfix: Fix userlog panic
+
+userlog services paniced because of `nil` ctx. That is fixed now
+
+https://github.com/owncloud/ocis/pull/6114

services/userlog/pkg/service/service.go

@@ -352,6 +352,10 @@ func (ul *UserlogService) resolveID(ctx context.Context, userid *user.UserId, gr
 		return []string{userid.GetOpaqueId()}, nil
 	}
 
+	if ctx == nil {
+		return nil, errors.New("need ctx to resolve group id")
+	}
+
 	return ul.resolveGroup(ctx, groupid.GetOpaqueId())
 }