class_docstr: Use Bert to generate words.
  
  Example::
  
      小明喜欢看书 -> 小明喜欢看报纸
code: def check(start, end, mask):
      for i in range(start, end + 1):
          if mask[i] != ORIGIN:
              return False
      return True
  
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 7 for calling the CnMLM obj's underlying member method code with example usage: obj.check(start, end, mask) and returns: True, False