docs: @Override
      public void doGet(HttpServletRequest req, HttpServletResponse res) throws IOException, ServletException {
  
          // check the error status
          Integer errorStatus = (Integer)req.getAttribute(CmsJspStatusBean.ERROR_STATUS_CODE);
          if (errorStatus != null) {
              // only use super method if an error status code is set
              if (OpenCmsCore.getInstance().getRunLevel() > OpenCms.RUNLEVEL_3_SHELL_ACCESS) {
                  // use super method if servlet run level is available
                  super.doGet(req, res);
              } else {
                  // otherwise display a simple error page
                  String errorMessage = (String)req.getAttribute(CmsJspStatusBean.ERROR_MESSAGE);
                  if (CmsStringUtil.isEmptyOrWhitespaceOnly(errorMessage)) {
                      errorMessage = "";
                  }
                  String output = "<html><body>"
                      + CmsStringUtil.escapeHtml(
                          Messages.get().getBundle().key(
                              Messages.ERR_OPENCMS_NOT_INITIALIZED_2,
                              errorStatus,
                              errorMessage))
                      + "</body></html>";
                  res.setStatus(errorStatus.intValue());
                  res.getWriter().println(output);
              }
          } else {
              // no status code set, this is an invalid request
              res.sendError(HttpServletResponse.SC_FORBIDDEN);
          }
      }