code: public GroupZipper right() {
          if (!canRight()) {
              throw new NoSuchElementException("Could not move right because the last node at this level has already been reached");
          }
  
          index++;
          node = parent.getNode().getGroups().get(index);
  
          return this;
      }
docs: Navigates right the tree to the next node at the same level.
  
  @return a new groupzipper which points to next node at the same level
  @throws NoSuchElementException
  if the last node at the current level has already been
  reached