BertForMaskedLM train
I have a question
When training using BertForMaskedLM, is the train data as below correct?
 - token2idx
```
<pad> : 0, <mask>: 1, <cls>:2, <sep>:3
```
 - max len : 8
 - input token
```
 <cls> hello i <mask> cats <sep>
```
 - input ids
```
 [2, 34,45,1,56,3,0,0]
```
 - attention_mask
```
 [1,1,1,1,1,1,0,0]
```
 - labels
```
 [-100,-100,-100,64,-100,-100,-100,-100]
```

I wonder if I should also assign -100 to labels for padding token.
Hello, thanks for opening an issue! We try to keep the github issues for bugs/feature requests.
Could you ask your question on the [forum](https://discusss.huggingface.co) instead?

Thanks!