code: @SuppressWarnings("unused")
      private Object readResolve() {
          if (StringUtils.isNotEmpty(oldTopic)) {
              oldTopicObject = new Topic(oldTopic);
              oldTopic = null;
          }
  
          if (oldTopicObject != null && StringUtils.isEmpty(oldTopicObject.getName())) {
              oldTopicObject = null;
          }
  
          return this;
      }
docs: Converts old serialized data to newer construct.
  
  @return itself