Adding Serial Type

Pretty basic question. Is it necessary to add NOT NULL or UNIQUE NOT
NULL to SERIAL or is this implicit and unnecessary?

ie.

CREATE TABLE new_table (
    id                             SERIAL UNIQUE NOT NULL,
    description             TEXT NOT NULL
);

Or should I just use below because Serial type implies this.

CREATE TABLE new_table (
    id                             SERIAL,
    description             TEXT NOT NULL
);


Regards,
David