> The only way to test is to specify
> 'SELECT * FROM TEST WHERE A IS NULL'.

That's true for explicit SQL statements but I think the same should be
possible using a parameter. At least in Delphi's TQuery it works with
Params[xx].Clear so I expected it from IBO, too.
It's convenient because you don't need to change the SQL statement text and
therefore Unprepare and Prepare again when looking for rows with NULL
fields.

Cheers,
TOndrej