select NOT IN with NULL bug on 7.2b3

Hi,
it is a bug ??

create table test (t1 int4, t2 int4);
insert into test values (1,1);
insert into test values (2,2);
insert into test values (3,1);
insert into test values (4,1);
insert into test values (4,1);
insert into test values (4,null);

select * from test where t1 not in (select t2 from test);
0 rows
select * from test where t1 not in (select null);
0 rows

If I delete the row with null value it works as expected.
The IN clause work as expected with or without null row.

sorry for my english.
bye

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