Should I be able to use NOT and null safe compare?

I can work around with colum1 is not null and column2 is null... but should it work with NOT (column1 <=> column2)? Here's an example.

MariaDB> CREATE TABLE cs1 (
    ->     id              INT(10) UNSIGNED NOT NULL,
    ->     `timestamp_`    DATETIME,
    ->     numeric_val     DOUBLE DEFAULT NULL
    -> ) ENGINE=columnstore;
Query OK, 0 rows affected (0.44 sec)

MariaDB> CREATE TABLE cs2 (
    ->     id              INT(10) UNSIGNED NOT NULL,
    ->     `timestamp_`    DATETIME,
    ->     numeric_val     DOUBLE DEFAULT NULL
    -> ) ENGINE=columnstore;
Query OK, 0 rows affected (0.25 sec)

MariaDB> SELECT @@version,@@version_comment;
+---------------------+---------------------+
| @@version           | @@version_comment   |
+---------------------+---------------------+
| 10.2.10-MariaDB-log | Columnstore 1.1.2-1 |
+---------------------+---------------------+
1 row in set (0.00 sec)

MariaDB]> INSERT INTO cs1 VALUES (1, '2018-01-09 21:59:02', 11.11);
Query OK, 1 row affected (0.11 sec)

MariaDB> INSERT INTO cs2 VALUES (1, '2018-01-09 21:59:02', 22.22);
Query OK, 1 row affected (0.10 sec)

MariaDB> SELECT * FROM cs1
    ->     JOIN cs2 USING(id,timestamp_)
    -> ;
+----+---------------------+-------------+-------------+
| id | timestamp_          | numeric_val | numeric_val |
+----+---------------------+-------------+-------------+
|  1 | 2018-01-09 21:59:02 |       11.11 |       22.22 |
+----+---------------------+-------------+-------------+
1 row in set (0.04 sec)

MariaDB> SELECT * FROM cs1
    ->     JOIN cs2 USING(id,timestamp_)
    ->     WHERE cs1.numeric_val <=> cs2.numeric_val
    -> ;
Empty set (0.02 sec)

MariaDB> SELECT * FROM cs1
    ->     JOIN cs2 USING(id,timestamp_)
    ->     WHERE NOT (cs1.numeric_val = cs2.numeric_val)
    -> ;
+----+---------------------+-------------+-------------+
| id | timestamp_          | numeric_val | numeric_val |
+----+---------------------+-------------+-------------+
|  1 | 2018-01-09 21:59:02 |       11.11 |       22.22 |
+----+---------------------+-------------+-------------+
1 row in set (0.02 sec)

MariaDB> SELECT * FROM cs1
    ->     JOIN cs2 USING(id,timestamp_)
    ->     WHERE NOT (cs1.numeric_val <=> cs2.numeric_val)
    -> ;
ERROR 1815 (HY000): Internal error: IDB-2030: Predicate and Logic operators can not be used where an expression is expected.