code: def _get_custom_models(models):
      
      if models is None:
          models = Model.model_class_reverse_map.values()
  
      custom_models = OrderedDict()
      for cls in models:
          impl = getattr(cls, "__implementation__", None)
  
          if impl is not None:
              model = CustomModel(cls)
              custom_models[model.full_name] = model
  
      if not custom_models:
          return None
      return custom_models
docs: Returns CustomModels for models with a custom `__implementation__`