code: public void add(String cssClass) {
      if (StringUtils.isBlank(cssClass)) {
        return;
      }
      String[] parts = StringUtils.split(cssClass, " ");
      for (String part : parts) {
        items.add(StringUtils.trim(part));
      }
    }
docs: Add CSS class item. Empty/Null items are ignore.d
  @param cssClass Item