public function addGroup(ChildGroup $group)
    {
        if ($this->collGroups === null) {
            $this->initGroups();
        }

        if (!$this->getGroups()->contains($group)) {
            // only add it if the **same** object is not already associated
            $this->collGroups->push($group);
            $this->doAddGroup($group);
        }

        return $this;
    }