Sorry, I was working on some issues and didn't remember to answer 🙁
Your problem is related to this issue where the previous code add extra empty <option> tag which allows users to clear selected option. However, it's not the default behaviour of <select> tag because <select> only shows options and force users to choose one of them. So I made the code work the same way.
I suggest you switch to select_advanced which has option for users to clear the selection.
Actually I made it true by default in some of previous versions. But I received a feedback from an user that suggested to hide if by default to make it work exactly like before. So here is what we have now.