code: private void writeKind(JsonGenerator jsonGenerator, Object entity) throws IOException {
          jsonGenerator.writeFieldName(KIND);
          if (entity instanceof EntitySet) {
              jsonGenerator.writeObject(ENTITY_SET);
          } else {
              jsonGenerator.writeObject(SINGLETON);
          }
      }
docs: Writes the kind of the entity.
  
  @param jsonGenerator jsonGenerator
  @param entity        entity from the container