*
   * @since 10.0
   */
  public static final class Wrapper<T extends @Nullable Object> implements Serializable {
    /*
     * Equivalence's type argument is always non-nullable: Equivalence<Number>, never
     * Equivalence<@Nullable Number>. That can still produce wrappers of various types --
     * Wrapper<Number>, Wrapper<Integer>, Wrapper<@Nullable Integer>, etc. If we used just

      List<@Nullable String> listWithNulls = asList("a", null, "b");
      assertThrows(NullPointerException.class, () -> builder.addAll((List<String>) listWithNulls));
    }

    {
      ImmutableList.Builder<String> builder = ImmutableList.builder();
      Iterator<@Nullable String> iteratorWithNulls =
          Arrays.<@Nullable String>asList("a", null, "b").iterator();
      assertThrows(

    return super.containsAll(collection);
  }

  @Override
  public Iterator<E> iterator() {
    return asList(contents).iterator();
  }

  @Override
  public @Nullable Object[] toArray() {
    @Nullable Object[] result = new @Nullable Object[contents.length];
    arraycopy(contents, 0, result, 0, contents.length);
    return result;
  }

  /*

import org.jspecify.annotations.Nullable;

/**
 * Skeletal implementation of {@link NavigableMap}.
 *
 * @author Louis Wasserman
 */
@GwtIncompatible
abstract class AbstractNavigableMap<K extends @Nullable Object, V extends @Nullable Object>
    extends IteratorBasedAbstractMap<K, V> implements NavigableMap<K, V> {

  @Override
  public abstract @Nullable V get(@Nullable Object key);

  @Override

  public int compare(@Nullable Object left, @Nullable Object right) {
    return 0;
  }

  @Override
  public <E extends @Nullable Object> List<E> sortedCopy(Iterable<E> iterable) {
    return Lists.newArrayList(iterable);
  }

  @Override
  public <E> ImmutableList<E> immutableSortedCopy(Iterable<E> iterable) {
    return ImmutableList.copyOf(iterable);
  }

   */
  @CanIgnoreReturnValue // TODO(kak): consider removing this
  @Override
  protected final <T extends @Nullable Object> RunnableFuture<T> newTaskFor(Callable<T> callable) {
    return TrustedListenableFutureTask.create(callable);
  }

  @CanIgnoreReturnValue // TODO(kak): consider removing this
  @Override
  public ListenableFuture<?> submit(Runnable task) {
    return (ListenableFuture<?>) super.submit(task);

  /**
   * Creates a {@code ListenableFutureTask} that will upon running, execute the given {@code
   * Callable}.
   *
   * @param callable the callable task
   * @since 10.0
   */
  public static <V extends @Nullable Object> ListenableFutureTask<V> create(Callable<V> callable) {
    return new ListenableFutureTask<>(callable);
  }

  /**
   * Creates a {@code ListenableFutureTask} that will upon running, execute the given {@code

      }
    }
    return false;
  }

  @Override
  public boolean contains(@Nullable Object rowKey, @Nullable Object columnKey) {
    Map<C, V> row = safeGet(rowMap(), rowKey);
    return row != null && Maps.safeContainsKey(row, columnKey);
  }

  @Override
  public @Nullable V get(@Nullable Object rowKey, @Nullable Object columnKey) {
    Map<C, V> row = safeGet(rowMap(), rowKey);

    private static final AtomicReferenceFieldUpdater<Waiter, @Nullable Thread> waiterThreadUpdater =
        AtomicReferenceFieldUpdater.<Waiter, @Nullable Thread>newUpdater(
            Waiter.class, Thread.class, "thread");
    private static final AtomicReferenceFieldUpdater<Waiter, @Nullable Waiter> waiterNextUpdater =
        AtomicReferenceFieldUpdater.<Waiter, @Nullable Waiter>newUpdater(
            Waiter.class, Waiter.class, "next");

    return super.toString();
  }

  @Override
  public boolean equals(@Nullable Object o) {
    assertTrue(Thread.holdsLock(mutex));
    return super.equals(o);
  }

  @Override
  public int hashCode() {
    assertTrue(Thread.holdsLock(mutex));
    return super.hashCode();
  }

  @Override
  public boolean add(@Nullable E o) {
    assertTrue(Thread.holdsLock(mutex));
    return super.add(o);
  }