//data_null: Result := _IsType(op2) = data_null;
      data_null:
        begin
          case OpType of
            0: if _IsType(op2) = data_null then Result := True else Result := False;
            5: if _IsType(op2) <> data_null then Result := True else Result := False;
            1,2,3,4: Result := _IsType(op2) = data_null;
          end;
        end;