code: public static String appendSlash(String inputString) {
      Preconditions.checkNotNull(inputString);
  
      if (inputString.endsWith("/")) {
        return inputString;
      }
  
      return inputString + "/";
    }
docs: *
  Append a slash ie / at the end of input string.
  
  @param inputString Input string to append a slash to
  @return String with slash appened