*
   * @since 20.0
   */
  public static <T extends @Nullable Object> FluentIterable<T> concat(
      Iterable<? extends T> a, Iterable<? extends T> b) {
    return concatNoDefensiveCopy(a, b);
  }

  /**
   * Returns a fluent iterable that combines three iterables. The returned iterable has an iterator