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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _item_to_document_ref(iterator, item):
 """Convert Document resource to document ref. Args: iterator (google.api_core.page_iterator.GRPCIterator):
 iterator response item (dict):
 document resource """

    document_id = item.name.split(_helpers.DOCUMENT_PATH_DELIMITER)[-1]
    return iterator.collection.document(document_id)