using NULL in OCIBindByPos()

I now have doubts whether I'm using the right mechanism to set NULL values in OCIBindByPos().

What is the correct contents of a passed SQL_STR when one intends to set the respective column (INTEGER,DATE,VARCHAR) to NULL?

One might say "don't set it, skip it", but for symmetry reasons I'm always doing an INSERT on the full bind list and it would be very difficult

to fish out only those columns that are really set to something != NULL.

Help appreciated. Thanks.

Christoph