I have a Core UI multi select implemented this way:

<select class="form-multi-select" id="referrerMultiSelect"></select>

Then in js:

const referrerMultiSelect = document.querySelector('#referrerMultiSelect');
const referrersMultiSelect = new coreui.MultiSelect(referrerMultiSelect, {
    cleaner: true,
    search: true,
    selectionType: 'tags',
    searchPlaceholder: 'Select...',
    optionsMaxHeight: '200px',
    selectAll: true,
    selectAllLabel: 'Select all',
    options: getReferrersForSelectOptions(referrers)
});
// referrers is an array of elements which contain id and value keys

function getReferrersForSelectOptions(referrers) {
    return referrers
        .filter(referrer => referrer.value)
        .map(referrer => {
            return {
                value: referrer.id,
                text: referrer.value
            }
        });
}

Everything works fine, all the options get applied, but there is no ‘Select all’ option in the list. What am I doing wrong?