ADD COLUMN NOT NULL is expecting the new column has to have a default value.

MariaDB [mcs87_db]> CREATE TABLE t1 (c1 INT, c2 CHAR(1)) ENGINE=Columnstore;
Query OK, 0 rows affected (0.142 sec)

MariaDB [mcs87_db]> INSERT INTO t1 VALUES (1, 'a');
Query OK, 1 row affected (0.221 sec)

MariaDB [mcs87_db]> ALTER TABLE t1 ADD COLUMN c11 INT NOT NULL;
ERROR 1815 (HY000): Internal error: Table is not empty. New column has to have a default value if NOT NULL required.
MariaDB [mcs87_db]> ALTER TABLE t1 ADD COLUMN c22 CHAR NOT NULL;
ERROR 1815 (HY000): Internal error: Table is not empty. New column has to have a default value if NOT NULL required.
MariaDB [mcs87_db]>

InnoDB accepts by adding 0 or empty string into the new column added.