*
   * @throws NullPointerException if {@code element} is null
   */
  public static <E> ImmutableList<E> of(E element) {
    return new SingletonImmutableList<>(element);
  }

  /**
   * Returns an immutable list containing the given elements, in order.
   *
   * @throws NullPointerException if any element is null
   */

  }

  public void testToOptionalNull() {
    Stream<@Nullable Object> stream = Stream.of((Object) null);
    try {
      stream.collect(MoreCollectors.toOptional());
      fail("Expected NullPointerException");
    } catch (NullPointerException expected) {
    }
  }

  public void testToOptionalMultiple() {
    try {
      Stream.of(1, 2).collect(MoreCollectors.toOptional());
      fail("Expected IllegalArgumentException");

   *
   * @throws NullPointerException if {@code element} is null
   * @since 6.0 (source-compatible since 2.0)
   */
  public static <E> ImmutableMultiset<E> of(E element) {
    return copyFromElements(element);
  }

  /**
   * Returns an immutable multiset containing the given elements, in order.
   *
   * @throws NullPointerException if any element is null

   * When multiple elements are equivalent according to {@link Comparable#compareTo}, only the first
   * one specified is included.
   *
   * @throws NullPointerException if any element is null
   */
  public static <E extends Comparable<? super E>> ImmutableSortedSet<E> of(E e1, E e2) {
    return construct(Ordering.natural(), 2, e1, e2);
  }

  /**

      fail("expected NullPointerException");
    } catch (NullPointerException expected) {
    }
  }

  public void testBuilderAddCopiesHandlesNullsCorrectly() {
    ImmutableMultiset.Builder<String> builder = ImmutableMultiset.builder();
    try {
      builder.addCopies(null, 2);
      fail("expected NullPointerException");
    } catch (NullPointerException expected) {
    }
  }

    try {
      builder.put(null, 1);
      fail();
    } catch (NullPointerException expected) {
    }
    try {
      builder.putAll(null, Arrays.asList(1, 2, 3));
      fail();
    } catch (NullPointerException expected) {
    }
    try {
      builder.putAll(null, 1, 2, 3);
      fail();
    } catch (NullPointerException expected) {
    }
    try {

   *
   * @throws NullPointerException if any element is null
   */
  public static <E extends Comparable<? super E>> ImmutableSortedMultiset<E> of(
      E e1, E e2, E e3, E e4) {
    return copyOf(Ordering.natural(), Arrays.asList(e1, e2, e3, e4));
  }

  /**
   * Returns an immutable sorted multiset containing the given elements sorted by their natural
   * ordering.
   *
   * @throws NullPointerException if any element is null

   * @return the non-null reference that was validated
   * @throws NullPointerException if {@code reference} is null
   * @see Verify#verifyNotNull Verify.verifyNotNull()
   */
  @CanIgnoreReturnValue
  public static <T> T checkNotNull(@CheckForNull T reference) {
    if (reference == null) {
      throw new NullPointerException();
    }
    return reference;
  }

  /**

    try {
      builder.put(null, 1);
      fail();
    } catch (NullPointerException expected) {
    }
    try {
      builder.putAll(null, Arrays.asList(1, 2, 3));
      fail();
    } catch (NullPointerException expected) {
    }
    try {
      builder.putAll(null, 1, 2, 3);
      fail();
    } catch (NullPointerException expected) {
    }
    try {

      fail();
    } catch (NullPointerException expected) {
    }

    try {
      ImmutableSortedMap.of("one", 1, null, 2);
      fail();
    } catch (NullPointerException expected) {
    }
  }

  public void testOfNullValue() {
    try {
      ImmutableSortedMap.of("one", null);
      fail();
    } catch (NullPointerException expected) {
    }

    try {