langchain/chains/qa_with_sources/base.py/BaseQAWithSourcesChain/validate_naming
class BaseQAWithSourcesChain:    def validate_naming(cls, values: Dict) -> Dict:
        """Fix backwards compatability in naming."""
        if "combine_document_chain" in values:
            values["combine_documents_chain"] = values.pop("combine_document_chain")
        return values