There is a bug when an upload field is required. The client-side validation works well, but I have some bad effect on the server side.
The Upload component extends the AbstractField class, that implements the isRequired method (and returning always false). So if my field is required, when I create a ValidationDecorator, the field.isRequired return always false !
For other inputs, everything is OK, because they are extending the AbstractTextField class that override again the isRequired method (but with the expected behavior)