Why is this line commented out

http://cgit.drupalcode.org/migrate/tree/migrate_example/beer.install.inc#n235

Why is this line commented out.

Was getting issue while the line was commented

.

WD php: PDOException: SQLSTATE[42000]: Syntax error or access violation: 1171 All parts of a PRIMARY KEY must be NOT NULL; if you need NULL[error]
in a key, use UNIQUE instead: CREATE TABLE {migrate_example_beer_account} (
`aid` INT auto_increment DEFAULT NULL COMMENT 'Account ID', 
`status` INT NOT NULL COMMENT 'Blocked_Allowed', 
`posted` VARCHAR(255) NOT NULL COMMENT 'Registration date', 
`name` VARCHAR(255) NULL DEFAULT NULL COMMENT 'Account name (for login)', 
`nickname` VARCHAR(255) NULL DEFAULT NULL COMMENT 'Account name (for display)', 
`password` VARCHAR(255) NULL DEFAULT NULL COMMENT 'Account password (raw)', 
`mail` VARCHAR(255) NULL DEFAULT NULL COMMENT 'Account email', 
`sex` INT NULL DEFAULT NULL COMMENT 'Gender', 
`beers` VARCHAR(255) NULL DEFAULT NULL COMMENT 'Favorite Beers', 
PRIMARY KEY (`aid`)
) ENGINE = InnoDB DEFAULT CHARACTER SET utf8 COMMENT 'Beers accounts.';