Add validation to SupplementaryFile field
For a SupplementaryFiles field in the submission form, enabling the "Required" validation option in the form-builder has no effect. It will not give a warning or prevent the form being submitted if no files are attached.
The same issue probably exists for the VisualAbstract field type.
I (BW) have not tested whether the issue exists for a SupplementaryFiles or VisualAbstract field in the decision or review forms, and this should be tested, as the implementation is different for these.