NULL in CREATE TABLE

According to specifications at
http://www.postgresql.org/docs/user/sql-createtable.htm "CREATE TABLE"
command should accept "NULL" specifier, but I get a parse error every
time I try to use it... "NOT NULL" works just fine.

,----[ Snippage from psql session ]
| antipode=> create table tmp_table ( a char(3) null, b char(4) not null);
| ERROR: parser: parse error at or near "null"
| antipode=> create table tmp_table ( a char(3) not null, b char(4) not null);
| CREATE
`----

Is this a known problem or is something wrong on my side? I'm running
Postgres 6.5.3 on FreeBSD 4-S.

Thanks!
--
Arcady Genkin http://www.thpoon.com
Nostalgia isn't what it used to be.