class_docstr: Use Bert to generate words.
  
  Example::
  
      小明喜欢看书 -> 小明喜欢看报纸
code: def __repr__(self):
      return "CnMLM"
  
file_path: textflint/textflint/generation/transformation/CWS/cn_mlm.py
imports: import torch
  from transformers import BertTokenizer, BertForMaskedLM
  from ..transformation import Transformation
  from ....input.component.field.cn_text_field import CnTextField
  from ....common.preprocess.cn_processor import CnProcessor
  from ....common.settings import ORIGIN, MODIFIED_MASK
label_desc: Use image node_id 2 for calling the CnMLM obj's underlying member method code with example usage: obj.__repr__() and returns: str