private SimpleMessageGroup normalizeSimpleMessageGroup(SimpleMessageGroup messageGroup) {
   SimpleMessageGroup normalizedGroup = new SimpleMessageGroup(messageGroup.getGroupId());
   for (Message<?> message : messageGroup.getMessages()) {
     Message<?> normailizedMessage = this.normalizeMessage(message);
     normalizedGroup.add(normailizedMessage);
   }
   return normalizedGroup;
 }