code: def fillna(self, value):
          
          if not is_scalar(value):
              raise TypeError('Value to replace with is not a valid scalar')
  
          return Series(weld_replace(self.weld_expr,
                                     self.weld_type,
                                     default_missing_data_literal(self.weld_type),
                                     value),
                        self.index,
                        self.dtype,
                        self.name)
docs: Returns Series with missing values replaced with value.
  
          Parameters
          ----------
          value : {int, float, bytes, bool}
              Scalar value to replace missing values with.
  
          Returns
          -------
          Series
              With missing values replaced.