src/transformers/tokenization_utils_fast.py/PreTrainedTokenizerFast/_convert_token_to_id_with_added_voc
class PreTrainedTokenizerFast:    def _convert_token_to_id_with_added_voc(self, token: str) -> int:
        index = self._tokenizer.token_to_id(token)
        if index is None:
            return self.unk_token_id
        return index