how to set default null to an int column

export const comments = mysqlTable(
  'comments',
  {
    id: serial('id').primaryKey(),
    authorId: int('author_Id').notNull(),
    parentId: int('parent_id'),
});

export const comments = mysqlTable(
  'comments',
  {
    id: serial('id').primaryKey(),
    authorId: int('author_Id').notNull(),
    parentId: int('parent_id'),
});