a&gt; {

    private SafeHtml errorMessage;

    public ValidatableInputCell(String errorMessage) {
      super("change");
      if (template == null) {
        template = GWT.create(Template.class);
      }
      this.errorMessage = SimpleHtmlSanitizer.sanitizeHtml(errorMessage);
    }

    @Override
    public void onBrowserEvent(Context context, Element parent, String value,
        NativeEvent event, ValueUpdater&lt;String&gt; valueUpdater) {
      super.onBrowserEvent(context, parent, value, event, val