code: def _find_references(model_name, references=None):
      
      references = references or []
      references.append(model_name)
  
      ref = MODELS[model_name].get('reference')
      if ref is not None:
          _find_references(ref, references)
  
      parent_models = [m for m in references]
      parent_models.reverse()
  
      return parent_models
docs: Iterate over model references for `model_name`
      and return a list of parent model specifications (including those of
      `model_name`, ordered from parent to child).