private void writeExternalCollection(Element parentElement,
                                       Collection<String> collection,
                                       String collectionName,
                                       String itemName) {
    if (!collection.isEmpty()) {
      Element child = parentElement.getChild(getTagName());
      if (child == null) {
        child = new Element(getTagName());
        parentElement.addContent(child);
      }
      Element element = new Element(collectionName);
      for (String item : collection) {
        element.addContent(new Element(itemName).setAttribute(COLLECTION_ITEM_ATTRIBUTE, item));
      }
      child.addContent(element);
    }
  }
private void writeExternalCollection(Element parentElement,
                                       Collection<String> collection,
                                       String collectionName,
                                       String itemName)