Automatic Group / Role / Rights by "Null Property Result"?

I’ve set up some Roles using a Retrieved Property with a pretty complex relevance. This Property will give a result defining a “Management Role” for the client, with possibly multiple results, such as “Role1”, “Role2”, etc.

I find it’s easy to create Automatic Groups based on a value for one of these roles, using ‘Property “Management Role” equals “Role1”’ (or “contains” or “does not equal” or “does not contain”.

However I’d like to also create an Automatic Group for computers that return an empty result or no result for my Retrieved Property - to identify “Unmanaged Clients” to find any edge cases where my Property Relevance gives an error or empty result. I’d like to set up a Web Report to alert me whenever computers get added to this unmanaged group, but I don’t see a way to do that.

Is there any combination that gives a result like not exists (property relevance) whose (exists value of it) ? or do I need to copy the original property relevance into the group and update it myself?