#vulnerable code 
                             @Override
	public Object call() throws Exception {
		List<Object> info = U.list();

		for (GroupOf<?> group : Groups.all()) {
			List<? extends Manageable> items = group.items();

			if (U.notEmpty(items)) {
				List<String> columns = U.first(items).getManageableProperties();

				if (U.notEmpty(columns)) {
					addInfo(info, group, items, columns);
				}
			}
		}

		info.add(autoRefresh(2000));
		return multi(info);
	} 
                            #location 9 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                             @Override
	public Object call() throws Exception {

		List<Object> info = U.list();
		Collection<? extends GroupOf<?>> targetGroups = groups != null ? groups : Groups.all();

		for (GroupOf<?> group : targetGroups) {
			List<? extends Manageable> items = group.items();

			List<String> nav = U.list(group.kind());

			info.add(h2(group.kind()));

			addInfo(baseUri, info, nav, items);
		}

		info.add(autoRefresh(2000));
		return multi(info);
	}