JSON_MERGE requires at least two arguments in MySQL, but not in MariaDB

MySQL [test]> SELECT JSON_MERGE('a');

ERROR 1582 (42000): Incorrect parameter count in the call to native function 'JSON_MERGE'

MariaDB [test]> SELECT JSON_MERGE('a');

+-----------------+

| JSON_MERGE('a') |

+-----------------+

| ["a"]           |

+-----------------+

1 row in set (0.00 sec)