*
   * @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

   *
   * @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

   *
   * @throws NullPointerException if any of the provided iterators is null
   */
  @SafeVarargs
  public static <T extends @Nullable Object> Iterator<T> concat(Iterator<? extends T>... inputs) {
    return concatNoDefensiveCopy(Arrays.copyOf(inputs, inputs.length));
  }

  /**
   * Combines multiple iterators into a single iterator. The returned iterator iterates across the