private function validateArtifactIdsAreInUnassignedTopBacklog($ids, $user, $project)
 {
     try {
         $this->milestone_validator->validateArtifactIdsAreInUnassignedTopBacklog($ids, $user, $project);
     } catch (ArtifactIsNotInUnassignedTopBacklogItemsException $exception) {
         throw new RestException(409, $exception->getMessage());
     } catch (IdsFromBodyAreNotUniqueException $exception) {
         throw new RestException(409, $exception->getMessage());
     } catch (\Exception $exception) {
         throw new RestException(400, $exception->getMessage());
     }
 }