JSON_OBJECTAGG silently drops rows with NULL keys

DROP DATABASE IF EXISTS r4;
CREATE DATABASE r4;
USE r4;
CREATE TABLE t(id INT AUTO_INCREMENT PRIMARY KEY, k VARCHAR(10), v INT);
INSERT INTO t(k, v) VALUES ('a',1),('b',2),('a',3),('a',4),('c',NULL),(NULL,5),('b',NULL);
SELECT JSON_OBJECTAGG(k, v) FROM t WHERE id IN (1,3);
– MDB:

(invalid) MY:

SELECT JSON_VALID(JSON_OBJECTAGG(k, v)) FROM t WHERE id IN (1,3); – MDB: 1

– [M33] JSON_OBJECTAGG silently drops NULL-key rows
SELECT JSON_OBJECTAGG(k, v) FROM t WHERE id IN (5,6);
– MDB:

(the NULL-key row is lost) MY: ERROR 3158
SELECT JSON_OBJECTAGG(NULL, 1); – MDB: NULL MY: ERROR 3158