private static final Iterable<@Nullable Integer> ITERABLE_NULL = Arrays.asList((Integer) null);
  private static final Iterable<@Nullable Integer> ITERABLE_NULL_NULL =
      Arrays.asList((Integer) null, null);
  private static final Iterable<@Nullable Integer> ITERABLE_NULL_1 = Arrays.asList(null, 1);
  private static final Iterable<@Nullable Integer> ITERABLE_1_NULL = Arrays.asList(1, null);

       * we're copying into a `contents` array whose type allows it to contain nulls. Still, it's
       * worth noting that we promise not to put nulls into the array in the first `size` elements.
       * We uphold that promise here because our callers promise that `elements` will not contain
       * nulls in its first `n` elements.
       */
      System.arraycopy(elements, 0, contents, size, n);
      size += n;

    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);
  }

    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))

    if (entry == null) {
      return null;
    } else {
      delete(entry);
      entry.prevInKeyInsertionOrder = null;
      entry.nextInKeyInsertionOrder = null;
      return entry.value;
    }
  }

  @Override
  public void clear() {
    size = 0;
    Arrays.fill(hashTableKToV, null);
    Arrays.fill(hashTableVToK, null);
    firstInKeyInsertionOrder = null;

        current.elemCount = 0;
        // Also clear these fields so that one deleted Entry doesn't retain all elements.
        current.left = null;
        current.right = null;
        current.pred = null;
        current.succ = null;

        current = next;
      }
      successor(header, header);
      rootReference.clear();
    } else {

      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();

      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);
    }