docs: @Override
      public JspConfigDescriptor getJspConfigDescriptor() {
          if (withinContextInitOfProgAddListener) {
              throw new UnsupportedOperationException(MessageFormat.format(
                      nls.getString("Unsupported.op.from.servlet.context.listener"),
                      new Object[] {"getJspConfigDescriptor", lastProgAddListenerInitialized, getApplicationName()}));  // PI41941
          }
          JspConfigDescriptorImpl jspConfigDescriptor = new JspConfigDescriptorImpl(this);
          if (jspConfigDescriptor.getJspPropertyGroups().isEmpty() && jspConfigDescriptor.getTaglibs().isEmpty()) {
              return null;
          }
          return jspConfigDescriptor;
      }