Editor Widget adds empty string in a not nullable field

[MHahn]

I got a hosted feature service with a text field that is not nullable. 
I expect that when I create a new feature with the editor widget, I´m not able to save the feature without entering a value. But the editor enters a empty value! 



You can reproduce this on this map (I shared it with public, but I think you need at least an agol account)
NullableTestMap (arcgis.com)

Do I miss something when uploading the service?
Or is this behaviour "as expected", realy?