MariaDB STORED columns don't accept [NULL | NOT NULL]

[RyuDoizaki]

Issue Description

When using MariaDB and creating a STORED column, the correct SQL is not generate.
MariaDB STORED columns don't accept [NULL | NOT NULL].
https://mariadb.com/kb/en/generated-columns/

Expected Behavior

I hope it will generate the correct SQL.

Actual Behavior, Steps to Reproduce

Entity

@Entity('test')
export class TestEntity {

  @PrimaryGeneratedColumn({ type: 'int' })
  readonly id!: number;

  @Column({
    type: 'varchar',
    generatedType: 'STORED',
    asExpression: 'CONCAT(id, "-stored")',
  })
  stored = '';
}

Generated SQL

CREATE TABLE `test` (`id` int NOT NULL AUTO_INCREMENT, `stored` varchar(255) AS (CONCAT(id, "-stored")) STORED NOT NULL, PRIMARY KEY (`id`)) ENGINE=InnoDB

Error Message

error: Error: ER_PARSE_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 'NOT NULL, PRIMARY KEY (`id`)) ENGINE=InnoDB' at line 1

My Environment

Dependency	Version
Operating System	macOS Catalina 10.15.7
Node.js version	v14.16.0
Typescript version	v4.2.4
TypeORM version	v0.2.32

Additional Context

Relevant Database Driver(s)

• aurora-data-api
• aurora-data-api-pg
• better-sqlite3
• cockroachdb
• cordova
• expo
• mongodb
• mysql
• mariadb
• nativescript
• oracle
• postgres
• react-native
• sap
• sqlite
• sqlite-abstract
• sqljs
• sqlserver

Are you willing to resolve this issue by submitting a Pull Request?

• Yes, I have the time, and I know how to start.
• Yes, I have the time, but I don't know how to start. I would need guidance.
• No, I don't have the time, although I believe I could do it if I had the time...
• No, I don't have the time and I wouldn't even know how to start.