Zero-value 'required' choice resource fields trigger validator error

I have a choice resource field where one of the choice keys is the string '0'. If the field is required, the validator does not detect the '0' and thinks no value was submitted in the form. There must be an empty call instead of isset somewhere.

Also, dropdown resource fields add an extra empty option instead of selecting the first in the list by default or having a 'default' setting, and the same is the case for radio fields.