new_contents: import uuid
  
  
  def custom_receiver(sender, **kwargs):
      """
      Set `youyouid` field with custom uuid.uuid4() ;)
      """
      instance = kwargs['instance']
      field_name = instance._base64field_name
  
      if getattr(instance, field_name) in ['', None]:
          gen_uuid = str(uuid.uuid4())
  
          sender._default_manager.filter(pk=instance.pk).update(
              **{field_name: gen_uuid}
          )
  
subject: Add custom_receiver