BUG #6701: IS NOT NULL doesn't work on complex composites

The following bug has been logged on the website:

Bug reference: 6701
Logged by: Rikard Pavelic
Email address: rikard(dot)pavelic(at)zg(dot)htnet(dot)hr
PostgreSQL version: 9.1.3
Operating system: Windows 7
Description:

create type t AS (i int);
create type complex as (t t, i int);
create table bad(i int, c complex);

insert into bad values(1, null);
insert into bad values(1, ROW(null, 2));
insert into bad values(1, ROW(ROW(1), 2));

select * from bad;
select * from bad where c is null;

--This doesn't work as expected
select * from bad where c is not null;

--Fortunately a workaround
select * from bad where NOT c is null;