Ho to handle "---" in filter of Delete Query?

Hi guys

once again a question.

I got a MDO having 3 columns A B C.

In there is a dataset looking like ['a', NULL, NULL] what looks like ['a', '---', '---'] in MII.

Want to delete this using a Query.

My Fiterexpression looks like [A] = [Param.1] AND [B] = [Param.2] AND [C] = [Param.3]

Tried to pass "---", "", nothing...but nothing works.

Any idea?

Thanks for your support!