public function addSkillGroup(ChildSkillGroup $l)
    {
        if ($this->collSkillGroups === null) {
            $this->initSkillGroups();
            $this->collSkillGroupsPartial = true;
        }

        if (!$this->collSkillGroups->contains($l)) {
            $this->doAddSkillGroup($l);
        }

        return $this;
    }