code: def _multiple_self_ref_fk_check(class_model):
      
      self_fk = []
      for f in class_model._meta.concrete_fields:
          if f.related_model in self_fk:
              return True
          if f.related_model == class_model:
              self_fk.append(class_model)
      return False
docs: We check whether a class has more than 1 FK reference to itself.