code: @Override
      protected void addIndex(Content body) {
          for (String groupname : groupList) {
              SortedSet<ModuleElement> list = groupModuleMap.get(groupname);
              if (list != null && !list.isEmpty()) {
                  addIndexContents(list,
                          groupname, configuration.getText("doclet.Member_Table_Summary",
                                  groupname, configuration.getText("doclet.modules")), body);
              }
          }
      }
docs: Add the module index.
  
  @param body the documentation tree to which the index will be added