issue of run_mlm.py 
hello guys, I try to finetune bert in my own dataset (line by line txt, language:Chinese), follow the guid code of run_mlm.py example.
The tokenizer is bert pretrained tokenizer (tokenizer=AutoTokenizer.from_pretrained('bert-base-chinese')), and model is bert-base-chinese ,as folllows:
    config=BertConfig.from_pretrained('bert-base-chinese')
    print(config)
    model=BertForMaskedLM(config=config)
when I started the trainer, I got the following errors:

Using custom data configuration default-cd6deed448eea358
Downloading and preparing dataset text/default (download: Unknown size, generated: Unknown size, post-processed: Unknown size, total: Unknown size) to /home/hcl/.cache/huggingface/datasets/text/default-cd6deed448eea358/0.0.0/293ecb642f9fca45b44ad1f90c8445c54b9d80b95ab3fca3cfa5e1e3d85d4a57...
                                Dataset text downloaded and prepared to /home/hcl/.cache/huggingface/datasets/text/default-cd6deed448eea358/0.0.0/293ecb642f9fca45b44ad1f90c8445c54b9d80b95ab3fca3cfa5e1e3d85d4a57. Subsequent calls will reuse this data.
100%|██████████| 3264/3264 [01:06<00:00, 48.83ba/s]
  0%|          | 0/3264 [00:00<?, ?ba/s]
Traceback (most recent call last):
  File "/home/hcl/miniconda3/envs/pytorch/lib/python3.7/site-packages/datasets/arrow_dataset.py", line 1582, in _map_single
    writer.write_batch(batch)
  File "/home/hcl/miniconda3/envs/pytorch/lib/python3.7/site-packages/datasets/arrow_writer.py", line 276, in write_batch
    pa_table = pa.Table.from_pydict(typed_sequence_examples)
  File "pyarrow/table.pxi", line 1559, in pyarrow.lib.Table.from_pydict
  File "pyarrow/array.pxi", line 331, in pyarrow.lib.asarray
  File "pyarrow/array.pxi", line 222, in pyarrow.lib.array
  File "pyarrow/array.pxi", line 110, in pyarrow.lib._handle_arrow_array_protocol
  File "/home/hcl/miniconda3/envs/pytorch/lib/python3.7/site-packages/datasets/arrow_writer.py", line 98, in __arrow_array__
    if trying_type and out[0].as_py() != self.data[0]:
  File "pyarrow/array.pxi", line 1067, in pyarrow.lib.Array.__getitem__
  File "pyarrow/array.pxi", line 549, in pyarrow.lib._normalize_index
IndexError: index out of bounds
python-BaseException

for now, I don't know why, the first epoch runs well. 
Any helps?
ps: my os is deepin15; I choose nvidia rtx2080ti as my gpu, and finetune my dataset on pytorch1.6
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