public function setPositionObjectInteractions(PositionObjectInteractionCollection $positionObjectInteractions)
    {
        if (count($positionObjectInteractions) > 0) {
            $this->positionObjectInteractions = $positionObjectInteractions;
        } else {
            $msg = "A PositionObjectStage object must be composed of at least 1 PositionObjectInteraction object, none given.";
            throw new InvalidArgumentException($msg);
        }
    }