How to init a subclass of BertForTokenClassification
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## Details
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I want to build a subclass of BertForTokenClassification and also want to use the weights of pretrained model
`
class SeqLabelClassifier(BertForTokenClassification):

    def __init__(self,  pretrained_model_name, config):
        super(SeqLabelClassifier,self).__init__(config)
        self.lstm=nn.LSTM(...)

config = BertConfig()
model = SeqLabelClassifier(pretrained_model_name, config)
model = model.from_pretrained(args.pretrained_model_name, config=config)
`
But I get this error

>   File "/home/haoran/anaconda3/envs/nsd/lib/python3.8/site-packages/transformers/modeling_utils.py", line 466, in from_pretrained
    model = cls(config, *model_args, **model_kwargs)
TypeError: __init__() missing 1 required positional argument: 'config'
How to correctly pass the args? 

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