If a boolean field is displayed but left empty, it creates a property with empty string as object

If opening a boolean input field by clicking on the plus symbol, but then not selecting either option in it, a triple with the respective property and with an empty string as object is created when saving the annotation. Instead, this triple should not be created.

I couldn't replicate this issue with other kinds of properties (text literals and autocomplete), so it might be working correct with those.