Predicate<@Nullable Integer> isNull = Predicates.equalTo(null);
    assertTrue(isNull.apply(null));
    assertFalse(isNull.apply(1));
  }

  public void testIsEqualToNull_equality() {
    new EqualsTester()
        .addEqualityGroup(
            Predicates.<@Nullable Integer>equalTo(null),
            Predicates.<@Nullable Integer>equalTo(null))
        .addEqualityGroup(Predicates.equalTo(1))

      int size = (keyList == null) ? 0 : keyList.count;
      checkPositionIndex(index, size);
      if (index >= (size / 2)) {
        previous = (keyList == null) ? null : keyList.tail;
        nextIndex = size;
        while (index++ < size) {
          previous();
        }
      } else {
        next = (keyList == null) ? null : keyList.head;
        while (index-- > 0) {
          next();

  @CollectionFeature.Require({SUPPORTS_ADD, ALLOWS_NULL_VALUES})
  public void testOffer_nullSupported() {
    assertTrue("offer(null) should return true", getQueue().offer(null));
    expectAdded((E) null);
  }

  @CollectionFeature.Require(value = SUPPORTS_ADD, absent = ALLOWS_NULL_VALUES)
  public void testOffer_nullUnsupported() {
    try {
      getQueue().offer(null);
      fail("offer(null) should throw");

      do {
        stack = head;
        if (stack == null) {
          // If head == null then execute() has been called so we should just return
          return;
        }
        // try to swap null into head.
      } while (!UNSAFE.compareAndSwapObject(this, HEAD_OFFSET, stack, null));

      RunnableExecutorPair reversedStack = null;
      while (stack != NULL_PAIR) {
        RunnableExecutorPair head = stack;

      return;
    }

    map.put(null, unmappedValue);
    assertEquals(unmappedValue, map.get(null));
    assertTrue(map.containsKey(null));
    Entry<@Nullable K, V> entry = mapEntry(null, unmappedValue);
    assertTrue(entrySet.remove(entry));
    assertNull(map.get(null));
    assertFalse(map.containsKey(null));
  }

  public void testEntrySetRemoveNullKeyMissing() {

    if (initialCapacity != null) {
      builder.initialCapacity(initialCapacity);
    }
    if (maximumSize != null) {
      builder.maximumSize(maximumSize);
    }
    if (maximumWeight != null) {
      builder.maximumWeight(maximumWeight);
    }
    if (concurrencyLevel != null) {
      builder.concurrencyLevel(concurrencyLevel);
    }

  }

  @MapFeature.Require(ALLOWS_NULL_VALUE_QUERIES)
  public void testContains_nullNotContainedButAllowed() {
    assertFalse("containsValue(null) should return false", getMap().containsValue(null));
  }

  @MapFeature.Require(absent = ALLOWS_NULL_VALUE_QUERIES)
  public void testContains_nullNotContainedAndUnsupported() {

      cachingHashMap.remove(key);
      return null;
    }
  }

  @CanIgnoreReturnValue
  @Override
  public V put(K key, V value) {
    checkNotNull(key);
    checkNotNull(value);
    Timestamped<V> oldValue = cachingHashMap.put(key, new Timestamped<V>(value, ticker));
    if (oldValue == null) {
      return null;
    }

    int[] expected = {0, 1, 2, 1, 4, 5, 0};
    checkIndexOf(toTest, expected);
  }

  public void testIndexOfImpl_null() {
    List<String> toTest;
    try {
      toTest = createList(String.class, null, "A", "B", null, "C", null);
    } catch (NullPointerException e) {
      // example cannot handle nulls, test invalid
      return;
    }
    int[] expected = {0, 1, 2, 0, 4, 0};
    checkIndexOf(toTest, expected);
  }

  @CollectionSize.Require(absent = ZERO)
  public void testCompute_presentNullToNull() {
    // The spec is somewhat ambiguous about this case, but the actual default implementation
    // in Map will remove a present null.
    initMapWithNullValue();
    assertNull(
        "Map.compute(presentMappedToNull, functionReturningNull) should return null",
        getMap()