int expectedHashCode = 0;
    for (E element : elements) {
      expectedHashCode += ((element == null) ? 0 : element.hashCode());
    }

    elements.add(null);
    collection = getSubjectGenerator().create(elements.toArray());
    assertEquals(
        "A Set's hashCode() should be the sum of those of its elements (with "
            + "a null element counting as having a hash of zero).",
        expectedHashCode,
        getSet().hashCode());

          }
        },
        "HashMap w/out null keys",
        ALLOWS_NULL_VALUES);
  }

  private static Test testsForHashMapNullValuesForbidden() {
    return wrappedHashMapTests(
        new WrappedHashMapGenerator() {
          @Override
          Map<String, String> wrap(final HashMap<String, String> map) {
            if (map.containsValue(null)) {
              throw new NullPointerException();

   *
   * @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
   * @since 6.0 (source-compatible since 2.0)
   */

    } catch (RuntimeException tolerated) {
      // GWT's TreeMap.entrySet().removeAll(null) doesn't throws NPE.
    }
  }

  @Override
  public void testEntrySetRetainAllNullFromEmpty() {
    try {
      super.testEntrySetRetainAllNullFromEmpty();
    } catch (RuntimeException tolerated) {
      // GWT's TreeMap.entrySet().retainAll(null) doesn't throws NPE.
    }
  }

  @Override

  }

  public void testOf_null() {
    try {
      Optional.of(null);
      fail();
    } catch (NullPointerException expected) {
    }
  }

  public void testFromNullable() {
    Optional<String> optionalName = Optional.fromNullable("bob");
    assertEquals("bob", optionalName.get());
  }

  public void testFromNullable_null() {
    // not promised by spec, but easier to test

      if (oldValue != null) {
        if (throwIfDuplicateKeys) {
          throw conflictException("key", entryArray[i], entryArray[i].getKey() + "=" + oldValue);
        }
        if (duplicates == null) {
          duplicates = new HashMap<>();
        }
        duplicates.put(key, value);
        dupCount++;
      }
    }
    if (duplicates != null) {
      @SuppressWarnings({"rawtypes", "unchecked"})

   */
  protected Entry<K, V>[] createArrayWithNullValue() {
    Entry<K, V>[] array = createSamplesArray();
    int nullValueLocation = getNullLocation();
    Entry<K, V> oldEntry = array[nullValueLocation];
    array[nullValueLocation] = Helpers.mapEntry(oldEntry.getKey(), null);
    return array;
  }

  /**

   * Equivalent to {@link #expectMissing(Object[]) expectMissing}{@code (null)} except that the call
   * to {@code contains(null)} is permitted to throw a {@code NullPointerException}.
   *
   * @param message message to use upon assertion failure
   */
  protected void expectNullMissingWhenNullUnsupported(String message) {
    try {
      assertFalse(message, actualContents().contains(null));
    } catch (NullPointerException tolerated) {

  private <T extends Iterator<E>> void internalExecuteAndCompare(
      T reference, T target, IteratorOperation method) {
    Object referenceReturnValue = null;
    PermittedMetaException referenceException = null;
    Object targetReturnValue = null;
    Exception targetException = null;

    try {
      targetReturnValue = method.execute(target);
    } catch (Exception e) { // sneaky checked exception
      targetException = e;

    @Override
    @CheckForNull
    public Integer next(Integer value) {
      int i = value;
      return (i == Integer.MAX_VALUE) ? null : i + 1;
    }

    @Override
    @CheckForNull
    public Integer previous(Integer value) {
      int i = value;
      return (i == Integer.MIN_VALUE) ? null : i - 1;
    }

    @Override
    Integer offset(Integer origin, long distance) {
      checkNonnegative(distance, "distance");