Not Validating Empty Fields

If I have a phone number field that is not required, I probably will want to allow it to be empty. A checkbox on the validator->field mapping page that said something like 'Do not run validation when empty' could solve this.

Without dependent validators, this almost unnecessary since using #required combined with the validator will be sufficient. With dependent validators though, you may want to run the validator even on an empty and non-required field since it's pass/fail would depend on a different field.