docs: def get_models(args):
      """
      Parse a list of ModelName, appname or appname.ModelName list, and return
      the list of model classes in the IndexRegistry. If the list if falsy,
      return all the models in the registry.
      """
      if args:
          models = []
          for arg in args:
              match_found = False
              for model in registry.get_models():
                  if model._meta.app_label == arg:
                      models.append(model)
                      match_found = True
                  elif '%s.%s' % (model._meta.app_label, model._meta.model_name) == arg:
                      models.append(model)
                      match_found = True
  
              if not match_found:
                  raise ValueError("No model or app named %s" % arg)
      else:
          models = registry.get_models()
  
      return set(models)