code: @Override
    public SoyMsgBundle exec(SoyNode node) {
      Preconditions.checkArgument(node instanceof SoyFileSetNode || node instanceof SoyFileNode);
  
      msgs = Lists.newArrayList();
      visit(node);
      Collections.sort(msgs, SOURCE_LOCATION_ORDERING);
      return new SoyMsgBundleImpl(null, msgs);
    }
docs: Returns a SoyMsgBundle containing all messages extracted from the given SoyFileSetNode or
  SoyFileNode (locale string is null).