* 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) {
    }
  }

   *
   * @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

    } catch (NullPointerException tolerated) {
    }
  }

  @CollectionFeature.Require(SUPPORTS_REMOVE)
  @CollectionSize.Require(absent = ZERO)
  public void testRetainAll_nullCollectionReferenceNonEmptySubject() {
    try {
      collection.retainAll(null);
      fail("retainAll(null) should throw NullPointerException");
    } catch (NullPointerException expected) {
    }
  }

   * @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 {

      getMap().replace(k0(), null);
      fail("Expected NullPointerException");
    } catch (NullPointerException expected) {
    }
    expectUnchanged();
  }

  @MapFeature.Require(value = SUPPORTS_PUT, absent = ALLOWS_NULL_VALUE_QUERIES)
  public void testReplace_absentNullValueUnsupported() {
    try {
      getMap().replace(k3(), null);
    } catch (NullPointerException tolerated) {

    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 {

    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 {