def _run_sync_callback(self, result: Any) -> CallbackReturn:
        """
        Runs the sync callback, if provided, and returns either a ToolOutput
        to override the default output or a string to override the content.
        """
        if self._callback:
            ret: CallbackReturn = self._callback(result)
            return ret
        return None

        Runs the sync callback, if provided, and returns either a ToolOutput
        to override the default output or a string to override the content.
        
llama-index-core/llama_index/core/tools/function_tool.py