try {
      builder.add((String) null);
      fail("expected NullPointerException"); // COV_NF_LINE
    } catch (NullPointerException expected) {
    }

    builder = this.<String>builder();
    try {
      builder.add((String[]) null);
      fail("expected NullPointerException"); // COV_NF_LINE
    } catch (NullPointerException expected) {
    }

    builder = this.<String>builder();
    try {

    try {
      builder.add((String) null);
      fail("expected NullPointerException"); // COV_NF_LINE
    } catch (NullPointerException expected) {
    }

    builder = this.<String>builder();
    try {
      builder.add((String[]) null);
      fail("expected NullPointerException"); // COV_NF_LINE
    } catch (NullPointerException expected) {
    }

    builder = this.<String>builder();
    try {

      try {
        entrySet.removeAll(null);
        fail("Expected NullPointerException.");
      } catch (NullPointerException expected) {
      }
    } else {
      try {
        entrySet.removeAll(null);
        fail("Expected UnsupportedOperationException or NullPointerException.");
      } catch (UnsupportedOperationException | NullPointerException e) {
        // Expected.
      }
    }
    assertInvariants(map);

   *
   * @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

   *
   * @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
   */

   * @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;
  }

  /**

      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 {

    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 {

    assertThrows(NullPointerException.class, () -> builder.add((String) null));
  }

  public void testBuilderAddAllHandlesNullsCorrectly() {
    {
      ImmutableSortedMultiset.Builder<String> builder = ImmutableSortedMultiset.naturalOrder();
      assertThrows(NullPointerException.class, () -> builder.addAll((Collection<String>) null));
    }

    {