Question about Upload component and submitUpload

Hi!
I have a task for uploading several files and data from form to server.
Task is stated such way, that user chooses several files, but uploading starts upon pressing submit button for all files at same time, and after this all data goes to database.
In theory i set immediate=false and use submitUpload for starting upload.
Ok.
I add events to detect problems in uploads and upload end, to submit data to database.
If i choose all files, all works perfectly, data is uploaded and submitted.

But only one file is mandatory, while i have several files on form, and they can be not provided.
If i don’t provide file, i don’t get any event after using submitUpload. No start, end or fail.

Is there any way to know on submitUpload, is file provided, or upload not started, or upload failed, or any other sign of abnormal upload process?

Hey Goergy

you have to look this page https://vaadin.com/book/-/page/components.upload.html -_-

good luck