What's the point of adding NOT NULL to primary key field in MySQL?

Question

What's the point of adding NOT NULL to a primary key field? Primary key is already not null + unique.

Here is an example:

CREATE TABLE student (
  id int(11) AUTO_INCREMENT NOT NULL,
  name varchar(255),
  PRIMARY KEY(id)
)

Why not to define it like this instead:

CREATE TABLE student (
  id int(11) AUTO_INCREMENT,
  name varchar(255),
  PRIMARY KEY(id)
)

Answer 1

They are the same. Primary key got NOT NULL automatically.

Answer 2

You are asking, why do people bother adding the NOT NULL when it is unnecessary? Just because it is good style, I guess. And makes it explicit to the reader.