code: private boolean sameTopic(HelpTopic topic1, HelpTopic topic2) {
          return topic1 == topic2 || (topic1 != null && topic2 != null && topic1.equals(topic2));
      }
docs: Because the HelpTopic class does not implement its own equals method, have to implement
  equality test here. Two topics are considered equal if the are the same instance or if their
  targets are equal.
  
  @param topic1 First topic to compare.
  @param topic2 Second topic to compare.
  @return True if topics are equal.