Issue #3306880 by alaeak.technalia: Autocomplete dragtable allows empty values...

    // Go two levels up in the form, to the widgets container.

    $element = NestedArray::getValue($form, array_slice($button['#array_parents'], 0, -2));

    // No value inserted on the input or empty value, we don't replace the

    // 'items-wrapper' element, this will prevent adding empty values.

    if ($element['add_more']['new_item']['target_id']['#value'] === '') {

      return $element;

    }

    // Remove the submitted value from the 'Add item' textfield.

    $element['add_more']['new_item']['target_id']['#value'] = NULL;