mlflow.langchain.autolog() raises ParentCommand Error when supervisor is about to handoff to subagent

[honghu-xue-ce]

Dear community,
I encounter a problem when the supervisor agent is about to handoff to its sub-agent. It raises an Parent Command Error (not sure whether it is an exception or an error). In my code, I set as follows:

mlflow.set_tracking_uri(MLFLOW_TRACKING_URI)
mlflow.set_experiment(EXPERIMENT_NAME)
mlflow.autolog(disable=True)
mlflow.langchain.autolog()

mlflow>=2.20.3
langgraph>=0.2.73
langchain>=0.3.19
langgraph-supervisor>=0.0.15

The error message is below. How to fix that error/exception?

The exception.message is shown as:
"Command(graph='parent', update={'messages': [HumanMessage(content='[]', additional_kwargs={}, response_metadata={}, id='856fbf56-ca9a-41fb-b8f0-cdb3cacb6c99'), AIMessage(content='', additional_kwargs={'tool_calls': [{'id': 'call_ TY0rtMbrfZesrWQd9GwM9', 'function': {'arguments': '{}', 'name': 'transfer_to_sub_agent'}, 'type': 'function'}], 'refusal': None}, response_metadata={'token_usage': {'completion_tokens': 14, 'prompt_tokens': 1968, 'total_tokens': 1982, 'completion_tokens_details': {'accepted_prediction_tokens': 0, 'audio_tokens': 0, 'reasoning_tokens': 0, 'rejected_prediction_tokens': 0}, 'prompt_tokens_details': {'audio_tokens': 0, 'cached_tokens': 0}}, 'model_name': 'gpt-4o-2024-11-20', 'system_fingerprint': '…’, 'finish_reason': 'tool_calls', 'logprobs': None, 'content_filter_results': {}}, name='supervisor', id=’…', tool_calls=[{'name': 'transfer_to_sub_agent', 'args': {}, 'id': 'call_ TY0rtMbrfZesrWQd9GwM9', 'type': 'tool_call'}], usage_metadata={'input_tokens': 1968, 'output_tokens': 14, 'total_tokens': 1982, 'input_token_details': {'audio': 0, 'cache_read': 0}, 'output_token_details': {'audio': 0, 'reasoning': 0}}), ToolMessage(content='Successfully transferred to sub_agent', name='transfer_to_sub_agent', tool_call_id='call_ TY0rtMbrfZesrWQd9GwM9')]}, goto='sub_agent')"

The exception.stacktrace is shown as:
"Traceback (most recent call last):\n File "/app/.venv/lib/python3.11/site-packages/langgraph/utils/runnable.py", line 608, in invoke\n input = step.invoke(input, config)\n ^^^^^^^^^^^^^^^^^^^^^^^^^^\n File "/app/.venv/lib/python3.11/site-packages/mlflow/utils/autologging_utils/safety.py", line 483, in safe_patch_function\n patch_function(call_original, *args, **kwargs)\n File "/app/.venv/lib/python3.11/site-packages/mlflow/langchain/_langchain_autolog.py", line 74, in patched_inference\n result = _invoke(self, *args, **kwargs)\n ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n File "/app/.venv/lib/python3.11/site-packages/mlflow/langchain/_langchain_autolog.py", line 66, in _invoke\n return original(self, *args, **kwargs)\n ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n File "/app/.venv/lib/python3.11/site-packages/mlflow/utils/autologging_utils/safety.py", line 474, in call_original\n return call_original_fn_with_event_logging(_original_fn, og_args, og_kwargs)\n ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n File "/app/.venv/lib/python3.11/site-packages/mlflow/utils/autologging_utils/safety.py", line 425, in call_original_fn_with_event_logging\n original_fn_result = original_fn(og_args, **og_kwargs)\n ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n File "/app/.venv/lib/python3.11/site-packages/mlflow/utils/autologging_utils/safety.py", line 471, in _original_fn\n original_result = original(_og_args, **_og_kwargs)\n ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n File "/app/.venv/lib/python3.11/site-packages/langgraph/utils/runnable.py", line 371, in invoke\n ret = context.run(self.func, *args, **kwargs)\n ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n File "/app/.venv/lib/python3.11/site-packages/langgraph/graph/branch.py", line 167, in _route\n result = self.path.invoke(value, config)\n ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n File "/app/.venv/lib/python3.11/site-packages/mlflow/utils/autologging_utils/safety.py", line 483, in safe_patch_function\n patch_function(call_original, *args, **kwargs)\n File "/app/.venv/lib/python3.11/site-packages/mlflow/langchain/_langchain_autolog.py", line 74, in patched_inference\n result = _invoke(self, *args, **kwargs)\n ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n File "/app/.venv/lib/python3.11/site-packages/mlflow/langchain/_langchain_autolog.py", line 66, in _invoke\n return original(self, *args, **kwargs)\n ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n File "/app/.venv/lib/python3.11/site-packages/mlflow/utils/autologging_utils/safety.py", line 474, in call_original\n return call_original_fn_with_event_logging(_original_fn, og_args, og_kwargs)\n ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n File "/app/.venv/lib/python3.11/site-packages/mlflow/utils/autologging_utils/safety.py", line 425, in call_original_fn_with_event_logging\n original_fn_result = original_fn(og_args, **og_kwargs)\n ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n File "/app/.venv/lib/python3.11/site-packages/mlflow/utils/autologging_utils/safety.py", line 471, in _original_fn\n original_result = original(_og_args, **_og_kwargs)\n ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n File "/app/.venv/lib/python3.11/site-packages/langgraph/utils/runnable.py", line 371, in invoke\n ret = context.run(self.func, *args, **kwargs)\n ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n File "/app/.venv/lib/python3.11/site-packages/langgraph/graph/state.py", line 1084, in control_branch\n raise ParentCommand(command)\nlanggraph.errors.ParentCommand: Command(graph='parent', update={'messages': [HumanMessage(content='[….]', additional_kwargs={}, response_metadata={}, id='…'), AIMessage(content='', additional_kwargs={'tool_calls': [{'id': …', 'function': {'arguments': '{}', 'name': 'transfer_to_subagent'}, 'type': 'function'}], 'refusal': None}, response_metadata={'token_usage': {'completion_tokens': 14, 'prompt_tokens': 1968, 'total_tokens': 1982, 'completion_tokens_details': {'accepted_prediction_tokens': 0, 'audio_tokens': 0, 'reasoning_tokens': 0, 'rejected_prediction_tokens': 0}, 'prompt_tokens_details': {'audio_tokens': 0, 'cached_tokens': 0}}, 'model_name': '…', 'system_fingerprint': '…, ', 'finish_reason': 'tool_calls', 'logprobs': None, 'content_filter_results': {}}, name='supervisor', id='…’, tool_calls=[{'name': 'transfer_to_sub_agent', 'args': {}, 'id': 'call_TY0rtMbrfZesrWQd9GwM9', 'type': 'tool_call'}], usage_metadata={'input_tokens': 1968, 'output_tokens': 14, 'total_tokens': 1982, 'input_token_details': {'audio': 0, 'cache_read': 0}, 'output_token_details': {'audio': 0, 'reasoning': 0}}), ToolMessage(content='Successfully transferred to sub_agent', name='transfer_to_sub_agent', tool_call_id='call TY0rtMbrfZesrWQd9GwM9')]}, goto='sub_agent')"