无法计算BELU

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日志如下:

sort: multi-character tab ‘$/t’
WARNING: 07-27 00:09:40: register.py:25 * 140311556190400 Key WordsegTokenizer already in registry tokenizer.
ERROR: 07-27 00:12:04: custom_static_generation_trainer.py:113 * 140311556190400 traceback.format_exc():Traceback (most recent call last):
File "/mnt/ernie-gen/applications/tasks/text_generation/trainer/custom_static_generation_trainer.py", line 94, in do_train
self.do_evaluate(self.data_set_reader.dev_reader, InstanceName.EVALUATE, steps)
File "/mnt/ernie-gen/applications/tasks/text_generation/trainer/custom_static_generation_trainer.py", line 157, in do_evaluate
self.model_class.get_metrics(fetch_output_dict, meta_info, phase, reader)
File "/mnt/ernie-gen/applications/tasks/text_generation/model/ernie_infilling_generation.py", line 496, in get_metrics
eval_res = self.eval.eval(outfile, phase, reader.features[phase])
File "/mnt/ernie-gen/erniekit/metrics/gen_eval.py", line 62, in eval
eval_res[mertric] = eval_func(refs, preds)
File "/mnt/ernie-gen/erniekit/metrics/gen_eval.py", line 75, in bleu
return _compute_bleu(refs, preds, max_order=4)[0]
File "/mnt/ernie-gen/erniekit/metrics/gen_eval.py", line 126, in _compute_bleu
ratio = float(translation_length) / reference_length
ZeroDivisionError: float division by zero

无法计算BELU，但是最后能够得到预测模型的文件，请问是哪里出现了问题，