code: public GeneratedValue<Id<T>> getOrCreateGeneratedValue()
     {
        Node node = childNode.getOrCreate("generated-value");
        GeneratedValue<Id<T>> generatedValue = new GeneratedValueImpl<Id<T>>(this, "generated-value", childNode, node);
        return generatedValue;
     }
docs: If not already created, a new <code>generated-value</code> element with the given value will be created.
  Otherwise, the existing <code>generated-value</code> element will be returned.
  @return  a new or existing instance of <code>GeneratedValue<Id<T>></code>