code: def na_rep(self) -> str:
      return self.fmt.na_rep
  
imports: from __future__ import annotations
  from collections.abc import Hashable, Iterable, Iterator, Sequence
  import csv
  import os
  from typing import TYPE_CHECKING, Any, cast
  import numpy
  from pandas._libs import writers
  from pandas._typing import SequenceNotStr
  from pandas.util._decorators import cache_readonly
  from pandas.core.dtypes.generic import ABCDatetimeIndex, ABCIndex, ABCMultiIndex, ABCPeriodIndex
  from pandas.core.dtypes.missing import notna
  from pandas.core.indexes.api import Index
  from pandas.io.common import get_handle
label_desc: Use image node_id 2 for calling the CSVFormatter obj's underlying member method code with example usage: obj.na_rep() and returns: self