CHECK (ISNULL(code)=ISNULL(class)) syntax error

It was working before until this version. The clause "CHECK (ISNULL(code)=ISNULL(class))" now causes syntax error mistakenly. Please refer to screen capture for problem explanation and replication.

root@fusion:~# uname -a
Linux fusion 5.4.0-53-generic #59~18.04.1-Ubuntu SMP Wed Oct 21 12:14:56 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux
root@fusion:~#
root@fusion:~# mysql fusion
Reading table information for completion of table and column names
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Welcome to the MariaDB monitor. Commands end with ; or \g.
Your MariaDB connection id is 39
Server version: 10.3.27-MariaDB-1:10.3.27+maria~bionic-log mariadb.org binary distribution

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MariaDB [fusion]> CREATE TABLE IF NOT EXISTS `test` (
-> `jmaster` varchar(18) COLLATE utf8_bin NOT NULL,
-> `class` varchar(2) COLLATE utf8_bin DEFAULT NULL,
-> `code` varchar(5) COLLATE utf8_bin DEFAULT NULL CHECK (ISNULL(code)=ISNULL(class)),
-> `id` int(11) NOT NULL AUTO_INCREMENT,
-> PRIMARY KEY (`id`)
-> ) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_bin;
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near '= (`class` is null)' at line 1
MariaDB [fusion]>