Can GROUP BY NULL when infinidb_vtable_mode=0

MariaDB [cs]> create table cs1(a varchar(1), i bigint) engine=columnstore;
Query OK, 0 rows affected (2.69 sec)

MariaDB [cs]> insert into cs1 values ('a',1),('b',2),('c',3),('d',4);
Query OK, 4 rows affected (0.43 sec)
Records: 4 Duplicates: 0 Warnings: 0

MariaDB [cs]> select a from cs1 group by a;
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4 rows in set (0.10 sec)

MariaDB [cs]> set infinidb_vtable_mode=1;
Query OK, 0 rows affected (0.00 sec)

MariaDB [cs]> select a from cs1 group by null;
ERROR 1178 (42000): The storage engine for the table doesn't support IDB-2016: Non supported item 'NULL' on the GROUP BY list.

MariaDB [cs]> set infinidb_vtable_mode=0;
Query OK, 0 rows affected (0.00 sec)

MariaDB [cs]>
MariaDB [cs]> select a from cs1 group by null;
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1 row in set (0.02 sec)