column definition: NOT NULL DEFAULT NULL

[lampcms.com]

Hello!
I've been using mysql for almost 10 years but never even thought about this
commonly seen column definition:
For example, column can be defined like this:
'email_address char(100) NOT NULL DEFAULT NULL'

Can someone exaplain this contradictory statement: how can the column be declared as NOT NULL and at the same type have a default value NULL?
Isnt' NOT NULL mean that value cannot be NULL?
Then how is it possible to have default value as NULL?

I just never thought about it until today, now it's finally time to find the answer.

I hope someone here can explain this really well. Thanks.

[swampBoogie]

It just means that if you do not supply a value for that column when doing insert, the DBMS will attempt to insert null which will cause an error. I.e. you are obliged to provide a non null value for that column when doing insert.

[lampcms.com]

So, the NOT NULL DEFAULT NULL does not mean that if I don't provide a value, the NULL will be inserted, it means that if I don't provide a value there will be an error?

I've never thought of this. I have to test it to make sure, but it does sound like reasonable explanation.