node_info['start'] does not exist

[filmo]

From flask_demo.py

    response_json = {
        "text": str(response),
        "sources": [{"text": str(x.text), 
                     "similarity": round(x.score, 2),
                     "doc_id": str(x.id_),
                     "start": x.node_info['start'],
                     "end": x.node_info['end'],
                    } for x in response.source_nodes]
    }

When I run this, I get an error saying that 'start' is not a valid key. It would only work when I commented out both the 'start' and 'end' portions of the response.