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