code: @Override
      public List<String> toMessageList(Locale locale, UserMessages messages) {
          assertArgumentNotNull("locale", locale);
          assertArgumentNotNull("errors", messages);
          if (messages.isEmpty()) {
              return Collections.emptyList();
          }
          final List<String> messageList = new ArrayList<String>();
          final Iterator<UserMessage> ite = messages.accessByFlatIterator();
          while (ite.hasNext()) {
              messageList.add(resolveMessageText(locale, ite.next()));
          }
          return Collections.unmodifiableList(messageList);
      }
docs: ================