return null;
            }
        } else {
            throwValidationError(messages -> messages.addErrorsDesignFileIsUnsupportedType("designFileName"), this::asListHtml);
            return null;
        }

        final File parentFile = uploadFile.getParentFile();
        if (!parentFile.exists() && !parentFile.mkdirs()) {

     * message: This file type is unsupported.
     * </pre>
     * @param property The property name for the message. (NotNull)
     * @return this. (NotNull)
     */
    public FessMessages addErrorsDesignFileIsUnsupportedType(String property) {
        assertPropertyNotNull(property);
        add(property, new UserMessage(ERRORS_design_file_is_unsupported_type));
        return this;
    }

    /**