code: def is_model_registered(app_label, model_name):
      
      try:
          apps.get_registered_model(app_label, model_name)
      except LookupError:
          return False
      else:
          return True
docs: Checks whether the given model is registered or not.
  
      It is usefull to prevent Machina models for being registered if they are overridden by local
      apps.