message: Fixed: return undefined if array length is zero.
diff: @@ -105,6 +105,9 @@ export default function() {
  const idx = e.item.idx;
  let ret = this.opts.val;
  ret.splice(idx, 1);
  + if (!ret.length) {
  + ret = undefined;
  + }
  this.itemsOpened.splice(idx, 1);
  this.update();
  this.opts.onchange(this.opts.identifier, ret);
  