fix: MariaDB VIRTUAL + [NOT NULL|NULL] error (#7022)
fix: MariaDB VIRTUAL + [NOT NULL|NULL] error (#7022)

* Fix MariaDB VIRTUAL [NOT NULL|NULL] error

Fixes #2691

query failed: ALTER TABLE `customer` CHANGE `fullName` `fullName` varchar(255) AS (CONCAT(`firstName`, ' ', `lastName`)) VIRTUAL NULL
error: Error: 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 'NULL' at line 1

* slightly change code style to improve readability

Co-authored-by: Umed Khudoiberdiev <f8fa069d3c2bda228844594609aecec355ee0884@gmail.com>
typeorm/typeorm,typeorm/typeorm,typeorm/typeorm