how to reproduce
- go to the demo : https://demo.ametys.org/nightly-intranet-cms/intranet/index.html
- create a form
- insert a file field
- insert a phrase in the title wording a "l' " (see screenshot)
- make this field mandatory
- insert the form into a page
- go to preview
- click ok without adding an attachment
the form turns in the void