code: def _fillna(expr, value):
      
  
      if isinstance(expr, SequenceExpr):
          return FillNa(_input=expr, _fill_value=value, _data_type=expr.dtype)
      elif isinstance(expr, Scalar):
          return FillNa(_input=expr, _fill_value=value, _value_type=expr.dtype)
docs: Fill null with value.
  
      :param expr: sequence or scalar
      :param value: value to fill into
      :return: sequence or scalar