{self.agent.return_values[0]: observation},
                    "",
                )
        return None
    def _prepare_intermediate_steps(
        self, intermediate_steps: List[Tuple[AgentAction, str]]
    ) -> List[Tuple[AgentAction, str]]:
        if (
            isinstance(self.trim_intermediate_steps, int)
            and self.trim_intermediate_steps > 0
        ):
            return intermediate_steps[-self.trim_intermediate_steps :]
        elif callable(self.trim_intermediate_steps):
            return self.trim_intermediate_steps(intermediate_steps)
        else:
            return intermediate_steps