} else {
      builder
          .append(o.getClass().getName())
          .append("@")
          .append(Integer.toHexString(System.identityHashCode(o)));
    }
  }

  /** Helper for printing user supplied objects into our toString method. */
  @SuppressWarnings("CatchingUnchecked") // sneaky checked exception
  private void appendUserObject(StringBuilder builder, @CheckForNull Object o) {