Hi, I'm trying to create a form with mandatory multiselect: I want the user to be required to select at least one value (see snippet). If I try to submit the form without selecting anything in the multiselect, no validation popup is displayed and the browser console shows the following error: An invalid form control is not focusable.

Expected behavior

When you submitting a form, a popup "This field is required" should appear, like it does with text inputs.

Resources (screenshots, code snippets etc.)

https://mdbootstrap.com/snippets/standard/ilya/6223388