Cursor protocol returns empty string instead of NULL for super-aggregated column for SELECT WITH ROLLUP

CREATE TABLE `example1463` (

  `Customer` varchar(255) NOT NULL,

  `DeliveryStatus` varchar(255) NOT NULL,

  `OrderSize` int(11) NOT NULL

);

INSERT INTO example1463 VALUES ('Charlie', 'Success', 100);

INSERT INTO example1463 VALUES ('David', 'Success', 110);

INSERT INTO example1463 VALUES ('Charlie', 'Failed', 200);

INSERT INTO example1463 VALUES ('David', 'Success', 100);

INSERT INTO example1463 VALUES ('David', 'Unknown', 100);

INSERT INTO example1463 VALUES ('Edward', 'Success', 150);

INSERT INTO example1463 VALUES ('Edward', 'Pending', 150);

SELECT Customer, Success, SUM(OrderSize)

 FROM (SELECT Customer,

 CASE WHEN DeliveryStatus='Success' THEN 'Yes' ELSE 'No' END AS Success,

 OrderSize

 FROM example1463) as subQ

 GROUP BY Success, Customer

 WITH ROLLUP;

 DROP TABLE example1463;

Customer	Success	SUM(OrderSize)

Charlie	No	200

David	No	100

Edward	No	150

NULL	No	450

Charlie	Yes	100

David	Yes	210

Edward	Yes	150

NULL	Yes	460

NULL	NULL	910

Customer	Success	SUM(OrderSize)

Charlie	No	200

David	No	100

Edward	No	150

	No	450

Charlie	Yes	100

David	Yes	210

Edward	Yes	150

	Yes	460

		910