[GENERAL] NULL & NOT NULL

[Bill Sneed]

I'm  (1) new to postgres & (2) trying to "convert" the sample db found
in "The Practical SQL Handbook" Bowman, et al. to postgres.  When
trying to create the following table I get "parser: parse error at or
near 'null'" 

create table authors (
        au_id           char(11)        not null,
        au_lname        varchar(40)     not null,
        .
        .
        .
        zip             char(5)         null
);

The table creation works fine twith the NOT NULL but won't work with
the NULL.  
NULL is supported isn't it?  I can't see where I'm making a syntax
error.  Got me stumped.  TIA.

........Bill Sneed Prospect, Maine......