code: public String getBackStackDescription() {
      ArrayList<Screen> backStackCopy = new ArrayList<>(backStack);
      Collections.reverse(backStackCopy);
      String currentScreen = "";
      if (!backStackCopy.isEmpty()) {
        currentScreen = backStackCopy.remove(backStackCopy.size() - 1).toString();
      }
      return TextUtils.join(" > ", backStackCopy) + (backStackCopy.isEmpty() ? "" : " > ") + "[" + currentScreen + "]";
    }
docs: Returns a human-readable string describing the screens in this Navigator's back stack.
  
  @return a human-readable description of the back stack.