if (wtag.isMessageTag())
{
String messageKey = wtag.getAttributes().getString("key");
if ((messageKey == null) || (messageKey.trim().length() == 0))
{
throw new MarkupException(
"Wrong format of <wicket:message key='xxx'>: attribute 'key' is missing");
}
// If the key can't be resolved and the default is null, an
// exception will be thrown. Instead, we default to a unique