query on NULL colum ... cannot pick it up

I get a strange result upon querying DB records in which the column
(VARCHAR) is set to NULL by default

the generated query is :
SELECT * FROM `contents` WHERE `contents`.`type` IN ('Article') AND
(state <> 'draft');

when contents.state is NULL, then the record IS NOT selected
when contents.state is'' ( empty ) then the record is selected
( obviously when set to any other value too..)

is it the 'standard' behavior ? ( so I'll have to change the
default ..)
or should I modify /add anything in the query ?

thanks for feedback

Yes, it's how SQL works--NULL is 'unknown', so comparison with any value returns null. You need a SQL primer, and look especially for three-valued logic.

thanks .. I am using now a '' (empty) default and it works