def main_input(
        self, func: Callable, sig: Signature, bindings: BoundArguments
    ) -> serial_utils.JSON:
        """
        Determine the main input string for the given function `func` with
        signature `sig` after it is called with the given `bindings` and has
        returned `ret`.
        """

        if "messages" in bindings.arguments:
            messages = bindings.arguments["messages"]
            if len(messages) == 1:
                message = messages[0]
                if "content" in message:
                    return message["content"]

        return json_utils.jsonify(bindings.arguments)

        Determine the main input string for the given function `func` with
        signature `sig` after it is called with the given `bindings` and has
        returned `ret`.
        
src/apps/nemo/trulens/apps/nemo/tru_rails.py