/**
  * @param SkillRank $skillRank
  * @throws \DrdPlus\Skills\Exceptions\CanNotVerifyOwningSkill
  */
 private function guardRelatedSkillOfRank(SkillRank $skillRank)
 {
     if ($this !== $skillRank->getSkill()) {
         if (static::class !== get_class($skillRank->getSkill())) {
             throw new Exceptions\CanNotVerifyOwningSkill('New skill rank belongs to different skill class. Expected ' . static::class . ', got ' . get_class($skillRank->getSkill()));
         } else {
             throw new Exceptions\CanNotVerifyOwningSkill('New skill rank belongs to different instance of skill class ' . static::class);
         }
     }
 }