docs: def delete_external_nodes(sender, **kwargs):
      """ sync by deleting nodes from external layers when needed """
      node = kwargs['instance']
  
      if node.layer.is_external is False or not hasattr(node.layer, 'external') or node.layer.external.synchronizer_path is None:
          return False
  
      if hasattr(node, 'external') and node.external.external_id:
          push_changes_to_external_layers.delay(
              node=node.external.external_id,
              external_layer=node.layer.external,
              operation='delete'
          )