get type error when I run the example code of token classification
## Environment info
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- `transformers` version:4.0.0
- Platform:linux and macos
- Python version:3.7 and 3.8
- PyTorch version (GPU?):1.7.0

### Who can help
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 albert, bert, GPT2, XLM: @LysandreJik 
 tokenizers: @mfuntowicz
 Trainer: @sgugger
 Speed and Memory Benchmarks: @patrickvonplaten
 Model Cards: @julien-c
 TextGeneration: @TevenLeScao 
 examples/distillation: @VictorSanh
 nlp datasets: [different repo](https://github.com/huggingface/nlp)
 rust tokenizers: [different repo](https://github.com/huggingface/tokenizers)
 Text Generation: @patrickvonplaten @TevenLeScao
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## Information


The problem arises when using:
hf_argparser in line 64. type Optional[bool] can not get into the loop 
elif field.type is bool or field.type is Optional[bool]

but after I change is to == ,the error disappear.

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Hi, could you provide the full error, as well as the command you use to launch the script? Thank you!<|||||>This issue has been automatically marked as stale because it has not had recent activity. If you think this still needs to be addressed please comment on this thread.

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