Binding String[] to checkbox-group

Hey guys, im trying to bind a string array to a checkbox group. The arrays fills with the values as it should when clicking the items but the clientside validation does not work. I cant find my mistake, can someone help out?

The field inside the java model:

  private String[] weeklyHours;

i tried “@NotNull” and “@Size” aswell but cant get the clientside validation to work…

The frontend code:

            <vaadin-checkbox value="20" label="20"></vaadin-checkbox>
            <vaadin-checkbox value="25" label="25"></vaadin-checkbox>
            <vaadin-checkbox value="30" label="30"></vaadin-checkbox>
            <vaadin-checkbox value="35" label="35"></vaadin-checkbox>
            <vaadin-checkbox value="40" label="40"></vaadin-checkbox>
            <vaadin-checkbox value="0" label="0"></vaadin-checkbox>

What i try to get is: when leaving all the checkboxes empty on submit, the group should be marked “red” like other form fields when violating the constraint

every other field/validation im using works fine its just the checkbox-group that wont work. Am i missing something? Thanks in advance