docs: public static String getBootstrapPage(CmsObject cms, Throwable throwable, HttpServletRequest request) {
  
          try {
              setErrorAttributes(cms, throwable, request);
  
              byte[] pageBytes = CmsFileUtil.readFully(
                  Thread.currentThread().getContextClassLoader().getResourceAsStream(
                      "org/opencms/ui/error/error-page.html"));
              String page = new String(pageBytes, "UTF-8");
              CmsMacroResolver resolver = new CmsMacroResolver();
              String context = OpenCms.getSystemInfo().getContextPath();
              String vaadinDir = CmsStringUtil.joinPaths(context, "VAADIN/");
              String vaadinVersion = Version.getFullVersion();
              String vaadinServlet = CmsStringUtil.joinPaths(context, "workplace/", ERROR_PAGE_PATH_FRAQUMENT);
              String vaadinBootstrap = CmsStringUtil.joinPaths(context, "VAADIN/vaadinBootstrap.js");
  
              resolver.addMacro("loadingHtml", CmsVaadinConstants.LOADING_INDICATOR_HTML);
              resolver.addMacro("vaadinDir", vaadinDir);
              resolver.addMacro("vaadinVersion", vaadinVersion);
              resolver.addMacro("vaadinServlet", vaadinServlet);
              resolver.addMacro("vaadinBootstrap", vaadinBootstrap);
              resolver.addMacro("title", "Error page");
  
              page = resolver.resolveMacros(page);
              return page;
          } catch (Exception e) {
              LOG.error("Failed to display error page.", e);
              return "<!--Error-->";
          }
      }