[Metric] Bertscore : Warning : Empty candidate sentence; Setting recall to be 0.
This print statement comes from the official implementation of bert_score (see [here](https://github.com/Tiiiger/bert_score/blob/master/bert_score/utils.py#L343)). The warning shows up only if the attention mask outputs no candidate.
Right now we want to only use official code for metrics to have fair evaluations, so I'm not sure we can do anything about it. Maybe you can try to create an issue on their [repo](https://github.com/Tiiiger/bert_score) ?
When running BERT-Score, I'm meeting this warning :

> Warning: Empty candidate sentence; Setting recall to be 0.

Code :

```
import nlp
metric = nlp.load_metric("bertscore")
scores = metric.compute(["swag", "swags"], ["swags", "totally something different"], lang="en", device=0)
```

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**What am I doing wrong / How can I hide this warning ?**