code: @Nullable
      public static String ensureEndsWith(@CheckForNull String subject, @CheckForNull String suffix) {
  
          if (subject == null) return null;
  
          if (subject.endsWith(suffix)) return subject;
  
          return subject + suffix;
      }
docs: Ensure string ends with suffix
  
  @param subject Examined string
  @param suffix  Desired suffix
  @return Original subject in case it already ends with suffix, null in
  case subject was null and subject + suffix otherwise.
  @since 1.505