Can't use NULL in IN conditional?

Charles Tassell (ctassell(at)isn(dot)net) reports a bug with a severity of 3
The lower the number the more severe it is.

Short Description
Can't use NULL in IN conditional?

Long Description
I don't know if this is a "feature" that comes alogn with NULL values, or somethign I'm doing wrong, but I can't seem to search for the NULL value via a WHERE xx IN clause. I've re-written the query to use OR and it works fine then, but not with the IN clause. This is with Postgres 7.02 on a Linux system (PostgreSQL 7.0.2 on i686-pc-linux-gnu, compiled by gcc egcs-2.91.66)

Sample Code
CREATE TABLE product_types (
type_id serial,
code text
)
INSERT INTO product_types (code) VALUES ('0A');
INSERT INTO product_types (code) VALUES (NULL);
-- This works
SELECT type_id, code FROM product_types WHERE code = '0A' OR code = NULL;
-- This doesn't
SELECT type_id, code FROM product_types WHERE code IN ('OA', NULL);

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