def _main_output_attribute(self, ret: Any) -> Optional[str]:
        """Which attribute in ret contains the main output of this llama_index
        app.
        """

        if isinstance(ret, Response):  # query, aquery
            return "response"

        elif isinstance(
            ret, (AgentChatResponse, StreamingAgentChatResponse)
        ):  #  chat, achat, stream_chat
            return "response"

        elif isinstance(
            ret,
            (StreamingResponse, AsyncStreamingResponse),
        ):
            return "response_txt"  # note that this is only available after the stream has been iterated over

        return None
Which attribute in ret contains the main output of this llama_index
        app.
        
src/apps/llamaindex/trulens/apps/llamaindex/tru_llama.py