code: def na_rep(self):
      return self._na_rep
  
file_path: mars/mars/dataframe/reduction/str_concat.py
imports: from ...None import opcodes
  from ...core import OutputType
  from ...serialization.serializables import StringField
  from .core import DataFrameReductionOperand, DataFrameReductionMixin
label_desc: Use image node_id 3 for calling the DataFrameStrConcat obj's underlying member method code with example usage: obj.na_rep() and returns: self