code: def _item_to_document_ref(iterator, item):
      
      document_id = item.name.split(_helpers.DOCUMENT_PATH_DELIMITER)[-1]
      return iterator.collection.document(document_id)
docs: Convert Document resource to document ref.
  
      Args:
          iterator (google.api_core.page_iterator.GRPCIterator):
              iterator response
          item (dict): document resource