How to report on blank Used By Name in Assets

[Frank Reay]

I want to run a report on certain Assets which do not have a Used By Name. I know that when the field is empty it is not Null but just has no value. However this does not work:

So I tried Prompted Value, and entered nothing when prompted, and that does work. But I want to run this as a scheduled job without any prompt - how do I achieve that?

[Frank Reay]

Found it:

So that is 2 single quotes together.