Sounds like it

You have to put something in the value



I tried alt+0160 in just the display w/value blank and in both, in both cases designer said topmost was unused.



So, I guess to allow a lookup here, I'm going to have to change my BO to return some known value if the field is null, then use that as my top most? I.e.



In BO define "NULL" as return if field is null and have BO save null if value is "NULL" (new in 1.6 I believe)



In list define top most as Alt+0160,NULL



I was using String.Empty in the BO, but no way to use that with a lookup. Am I on the right track here?

You can't use a space, you have to use the Alt+0160 character.  Just go to the property and rather than trying to use a space, just put the Alt+0160 in the display value.  If you do that you might be able to leave the value empty...I haven't test that.  Worst case you can do the same thing on the value.

I'd like to have my top most item be an empty string for both the display and the value. I tried String.Empty and "" both of which didn't work. String.Empty actually put the string 'String.Empty' in the combo and "" put the string '""' (set of double quotes).



So, how would I do this?