class CatalogIdentifierDatasource extends SlingSafeMethodsServlet {

    @Override
    protected void doGet(@Nonnull SlingHttpServletRequest request, @Nonnull SlingHttpServletResponse response) throws ServletException,
        IOException {
        DataSource ds;

        if (catalogIdentifierService == null) {
            ds = EmptyDataSource.instance();
        } else {
            ds = buildValuesList(request.getResourceResolver());
        }

        request.setAttribute(DataSource.class.getName(), ds);
    }

}