Issue with aggregation_strategy="max" in NER pipeline
## Environment info
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- `transformers` version: 4.17.0
- Python version: Python 3.7.13
- PyTorch version (GPU?): 1.10.0+cu111
- Using GPU in script?: NO
- Using distributed or parallel set-up in script?: NO

### Who can help
@LysandreJik
@Narsil
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## Information

Good day,

Up untill yesterday my NER model was working fine using the pipeline and the aggregation_strategy=“max”. Now, I get the error message: TypeError: Can’t convert [’ In’] to PyString which is the first word of my sentence.
I noticed that using “simple” it works fine, but for my system “max” was the best working one.
It seems to me that now the tokenizer is putting words in a list whereas before it didn’t.
Did something change in the use of the tokenizer or aggregation_stategy?
I can’t figure out why this is happening.
This is my model and code:

`tokenizer_mbert_mul = AutoTokenizer.from_pretrained("StivenLancheros/roberta-base-biomedical-clinical-es-finetuned-ner-CRAFT_AugmentedTransfer_ES")

model_mbert_mul = AutoModelForTokenClassification.from_pretrained("StivenLancheros/roberta-base-biomedical-clinical-es-finetuned-ner-CRAFT_AugmentedTransfer_ES")
ner = pipeline('ner', aggregation_strategy="max", model=model_mbert_mul, tokenizer=tokenizer_mbert_mul)`

## To reproduce

This a sentence of my data:

"“In biology, a gene (from genos (Greek) meaning generation or birth or gender) is a basic unit of heredity and a sequence of nucleotides in DNA that encodes the synthesis of a gene product”

This is the error message:

`/usr/local/lib/python3.7/dist-packages/transformers/tokenization_utils_fast.py in convert_tokens_to_string(self, tokens)
    533 
    534     def convert_tokens_to_string(self, tokens: List[str]) -> str:
--> 535         return self.backend_tokenizer.decoder.decode(tokens)
    536 
    537     def _decode(

TypeError: Can't convert [' In'] to PyString`
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## Expected behavior

It was producing NER with the correct aggregation_strategy, however now it does not. I downgraded to the transformers 4.16 version and it works just fine.


Might be worth trying to uninstall and reinstall `tokenizers`. Tokenizers 0.12 was yanked and a new version is coming. See #16520, #16525, #16537, #16540 for more. <|||||>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.

Please note that issues that do not follow the [contributing guidelines](https://github.com/huggingface/transformers/blob/main/CONTRIBUTING.md) are likely to be ignored.