If a file was not selected and the user clicks Upload button, the form sends an empty submit request. The form then changes to a loading state, while its waiting for a response. Since the request is empty, the form never gets a response. 

1 - If you click Upload button without selecting files, the modal box will gets destroyed: this can be fixed in gravy.modalBox.

2 - The Upload button is enabled when files are selected.

   2a - The form is submitted normally when clicking the Upload button. 

3 - The Upload button is disabled when files are not selected.