title: App is crashing if using Core Data (attribute of type boolean)
body: <p>I addded a new attribute (of type boolean) into my core data model and my data.swift class. I try to run my app after I added the attribute. All works fine. Now I try to work with the new attribute. I wrote some code, which work is working with the attribute. Now I tried a 2nd time to run the app. It's crashing. Does someone knows why? </p>