code: protected HelpTopic getTopic(TreeNode node) {
          try {
              DefaultMutableTreeNode nd = (DefaultMutableTreeNode) node;
              TreeItem item = (TreeItem) nd.getUserObject();
              ID id = item.getID();
              HelpTopic topic = new HelpTopic(id == null ? null : id.getURL(), item.getName(), view.getHelpSet().getTitle());
              
              if (id != null && view.getHelpSet().getKeyData("topics", id.id) == null) {
                  view.getHelpSet().setKeyData("topics", id.id, topic);
              }
              
              return topic;
          } catch (MalformedURLException e) {
              return null;
          }
      }
docs: Retrieves the help topic associated with the given node. Note that this also maintains a map
  of topic id --&gt; topic mappings in the parent help set.
  
  @param node Tree node.
  @return A help topic instance.