Selectivity renderItems

/**
 * Override default 'renderItems()' function of selectivity
 * to accept option with value='' (empty string, item.id === '') as a valid option.
 *
 * @param items Array of result items.
 * @returns HTML-formatted string to display the result items.
 */
$.Selectivity.Dropdown.prototype.renderItems = function (items) {
    const selectivity = this.selectivity;
    const originalEl = selectivity.options.element;
    const $optionElements = $(originalEl.options);
    const hasClass = $(originalEl).find('[data-class]').length;

    return items.map(function (item) {
        if (hasClass) {
            $optionElements.each(function (i, el) {
                const $el = $(el);
                const id = $el.val();
                if (id == item.id) {
                    item.cssClass = $(el).data('class');
                    return false
                }
            });
        }

        let result = selectivity.template(item.id === '' || item.id ? 'resultItem' : 'resultLabel', item);
        if (item.children) {
            result += selectivity.template('resultChildren', {
                childrenHtml: this.renderItems(item.children),
            });
        }
        return result;
    }, this).join('');
};