ArcGIS Online Filter Widget -empty- value

[LucasMurray2]

Not sure when this started or why but when I build a filter widget in the ArcGIS Online Web AppBuilder and set the expression to accept unique values, in the list of available values is one called "-empty-."  When I select this value in the filter, it apparently has the same effect as turning off the filter in that all features are shown on the map.  Is there a way to remove the -empty- option from the value list?  I want to force users to select a specific value in the filter and not have the ability to see all features on the map.

[MarkEastwood]

I am currently running into the same issue. Were you able to find a way to hide the -empty- value?