/**
     * Additional search fields for error page display.
     */
    public Map<String, String[]> fields = new HashMap<>();

    /**
     * Default constructor for ThumbnailForm.
     */
    public ThumbnailForm() {
        // Default constructor
    }

     * @return ActionResponse containing the thumbnail image or 404 if not found
     */
    @Execute
    public ActionResponse index(final ThumbnailForm form) {
        validate(form, messages -> {}, () -> asHtml(virtualHost(path_Error_ErrorJsp)));
        if (isLoginRequired()) {
            return redirectToLogin();
        }

        final Map<String, Object> doc =