src/transformers/models/bert/tokenization_bert_tf.py/TFBertTokenizer/unpaired_tokenize
class TFBertTokenizer:    def unpaired_tokenize(self, texts):
        if self.do_lower_case:
            texts = case_fold_utf8(texts)
        tokens = self.tf_tokenizer.tokenize(texts)
        return tokens.merge_dims(1, -1)