* @return the difference between the two maps
   * @since 11.0
   */
  public static <K extends @Nullable Object, V extends @Nullable Object>
      SortedMapDifference<K, V> difference(
          SortedMap<K, ? extends V> left, Map<? extends K, ? extends V> right) {
    checkNotNull(left);
    checkNotNull(right);