code: private Widget createDoubleWidget(DoubleAttribute attributeValue) {
  		VerticalPanel panel = new VerticalPanel();
  		String formattedNumber = NumberFormat.getDecimalFormat().format(attributeValue.getValue());
  		panel.getElement().setInnerText(formattedNumber);
  		return panel;
  	}
docs: Create a custom widget for attributes of type {@link Double}. Simply applies a number
  formatter on the attribute value and puts it in a panel.
  
  @param attributeValue the value of the attribute.
  @return the custom widget.