docs: def save_external_nodes(sender, **kwargs):
      """ sync by creating nodes in external layers when needed """
      node = kwargs['instance']
      operation = 'add' if kwargs['created'] is True else 'change'
  
      if node.layer.is_external is False or not hasattr(node.layer, 'external') or node.layer.external.synchronizer_path is None:
          return False
  
      push_changes_to_external_layers.delay(node=node, external_layer=node.layer.external, operation=operation)