Open form with either of two choices in Option Group?

[wrek]

On my main form, I have an option group (ACDFrame), with two choices: 1 and 2 (default value)

I have a button on the main form that opens Form 2.

If 1, I want to show all the records in the next form I open.

If 2, I want to show ONLY the records with NULL data in the field in question.

Here is what I have under the field (add chg del) in the query that Form 2 is linked to:

IIf([Forms]![Form - Master]![ACDFrame]=2,[Static TBL 0000010028 BOM May 10]![add chg del]='Is Null',[Static TBL 0000010028 BOM May 10]![add chg del])

My problem is that the True part of the IIf structure ([Static TBL 0000010028 BOM May 10]![add chg del]='Is Null') doesnt bring out the null records, it shows none.

The False part works.

Help anyone??