TypeError: 'NoneType' object is not iterable

[junming-yang]

Traceback (most recent call last):
  File "/home/miniconda3/envs/vllm/bin/alpaca_eval", line 8, in <module>
    sys.exit(main())
  File "/home/miniconda3/envs/vllm/lib/python3.10/site-packages/alpaca_eval/main.py", line 608, in main
    fire.Fire(ALL_FUNCTIONS)
  File "/home/miniconda3/envs/vllm/lib/python3.10/site-packages/fire/core.py", line 135, in Fire
    component_trace = _Fire(component, args, parsed_flag_args, context, name)
  File "/home/miniconda3/envs/vllm/lib/python3.10/site-packages/fire/core.py", line 468, in _Fire
    component, remaining_args = _CallAndUpdateTrace(
  File "/home/miniconda3/envs/vllm/lib/python3.10/site-packages/fire/core.py", line 684, in _CallAndUpdateTrace
    component = fn(*varargs, **kwargs)
  File "/home/miniconda3/envs/vllm/lib/python3.10/site-packages/alpaca_eval/main.py", line 155, in evaluate
    annotations = annotator.annotate_head2head(
  File "/home/miniconda3/envs/vllm/lib/python3.10/site-packages/alpaca_eval/annotators/pairwise_evaluator.py", line 237, in annotate_head2head
    out = self.__call__(df_to_annotate, **decoding_kwargs)
  File "/home/miniconda3/envs/vllm/lib/python3.10/site-packages/alpaca_eval/annotators/base.py", line 218, in __call__
    df_annotated = self._annotate(curr_df_to_annotate, **decoding_kwargs)
  File "/home/miniconda3/envs/vllm/lib/python3.10/site-packages/alpaca_eval/annotators/base.py", line 336, in _annotate
    curr_annotated = self.annotators[annotator](
  File "/home/miniconda3/envs/vllm/lib/python3.10/site-packages/alpaca_eval/annotators/base.py", line 718, in __call__
    completions = self.fn_completions(prompts=prompts, **self.completions_kwargs, **decoding_kwargs)
  File "/home/miniconda3/envs/vllm/lib/python3.10/site-packages/alpaca_eval/decoders/openai.py", line 153, in openai_completions
    completions = list(
  File "/home/miniconda3/envs/vllm/lib/python3.10/site-packages/tqdm/std.py", line 1181, in __iter__
    for obj in iterable:
  File "/home/miniconda3/envs/vllm/lib/python3.10/concurrent/futures/_base.py", line 621, in result_iterator
    yield _result_or_cancel(fs.pop())
  File "/home/miniconda3/envs/vllm/lib/python3.10/concurrent/futures/_base.py", line 319, in _result_or_cancel
    return fut.result(timeout)
  File "/home/miniconda3/envs/vllm/lib/python3.10/concurrent/futures/_base.py", line 458, in result
    return self.__get_result()
  File "/home/miniconda3/envs/vllm/lib/python3.10/concurrent/futures/_base.py", line 403, in __get_result
    raise self._exception
  File "/home/miniconda3/envs/vllm/lib/python3.10/concurrent/futures/thread.py", line 58, in run
    result = self.fn(*self.args, **self.kwargs)
  File "/home/miniconda3/envs/vllm/lib/python3.10/site-packages/alpaca_eval/decoders/openai.py", line 235, in _openai_completion_helper
    for i, choice in enumerate(choices):
TypeError: 'NoneType' object is not iterable

I have tried to print the choices. Most of the time, it works well but is stuck in some requests. Can you provide any suggestions for solving it?