We need this one to be removed in order to tell the user which ID's are invalid. If we keep this one silent it will have the benefit you describe where the empty warning won't be shown when the user opens the control but, the user will not be alerted as to which of their ID's are invalid and the Apply Filter button won't become enabled until they figure out which are invalid. So, we either pester them with the empty message or we never alert them of their invalid filters. 

The validateFilter method could be updated to only return the empty message if the filter is already applied _and_ the value is empty. Does that make sense?