/**
  * @throws IdsFromBodyAreNotUniqueException
  * @throws ArtifactDoesNotExistException
  * @throws ArtifactIsNotInBacklogTrackerException
  * @throws ArtifactIsClosedOrAlreadyPlannedInAnotherMilestone
  */
 public function validate(array $to_add)
 {
     $this->milestone_validator->validateArtifactsFromBodyContentWithClosedItems($to_add, $this->milestone, $this->user);
 }