The following CREATE TABLE statement creates a table called 'users' that consists of the user$\_$id as the primary key that is auto$-$incremented, the username, and the password.

CREATE TABLE users$($

user$\_$id serial PRIMARY KEY,

username VARCHAR $(50)$

password VARCHAR $(50)$

$)$;

Identify the line of code that would either generate a syntax, logical$,$ or requirements error in this CREATE TABLE statement.