Mandatory property not working on formFile

Steps to reproduce

1. Configure the formFile component to have a mandatory boolean property. Like formEdit.
2. Add the formFile component to any formulary with the new property set to true
3. Trying to submit the form, either with a file attached or not, will result on an error taking place.

Expected results

The form can't be submitted only if the file is not attached.

Actual results

The form can't be submitted wether the file is attached or not.

Workaround

Development notes

The check seems to take place here:

https://git.magnolia-cms.com/projects/MODULES/repos/form/browse/magnolia-form/src/main/java/info/magnolia/module/form/templates/components/DefaultFormDataBinder.java#152

The validation doesn't take into account that StringUtils.isEmpty will return null if the field is an attachment, resulting on it always returning an error.