code: private void writeURL(JsonGenerator jsonGenerator, Object entity) throws IOException {
          // It is exactly the same as the 'name' property.
          jsonGenerator.writeFieldName(URL);
          if (entity instanceof EntitySet) {
              jsonGenerator.writeObject(((EntitySet) entity).getName());
          } else {
              jsonGenerator.writeObject(((Singleton) entity).getName());
          }
      }
docs: Writes the url of the entity
  It is a MUST element.
  
  @param jsonGenerator jsonGenerator
  @param entity        entity from the container