None values in head_type and tail_type

[philippmaa]

Hi,

thank you very much for this very helpful library - I like it a lot!
Processing some documents I stumbled around a NoneType error during the validation of the Node BaseModel.

In the for-loop of LLMGraphTransformer -> process_response with self._function_call == False there is a check for None values of the head, tail and relation keys in the parsed_json. A few lines later there is:

source_node = Node(id=rel["head"], type=rel.get("head_type", DEFAULT_NODE_TYPE))

In my case it occurred, that rel["head_type"] is present but is None. In this case, rel.get("head_type", DEFAULT_NODE_TYPE) yields None instead of DEFAULT_NODE_TYPE and a pydantic.ValidatonError is raised.

Maybe there should be another sanity check like:

rel["head_type"] = rel.get("head_type", DEFAULT_NODE_TYPE) or DEFAULT_NODE_TYPE
rel["tail_type"] = rel.get("tail_type", DEFAULT_NODE_TYPE) or DEFAULT_NODE_TYPE

to make sure the type values are not None?

Best, Philipp