Comparing with NULL will resolve to NULL, which is neither True nor False.

You can change the query as follows:
Code
SELECT *
FROM
MYTAB A
WHERE
(A.COL1 = :COL1 OR (A.COL1 IS NULL AND :COL1 IS NULL))
AND
(A.COL2 = :COL2 OR (A.COL2 IS NULL AND :COL2 IS NULL))

Marco Kalter
Allround Automations