* objects per entry.  Instead we use an open-addressed hash table.  This design is basically
   * equivalent to RegularImmutableSet, save that instead of having a hash table containing the
   * elements directly and null for empty positions, we store indices of the keys in the hash table,
   * and ABSENT for empty positions.  We then look up the keys in alternatingKeysAndValues.
   *

   * cannot implement that interface in source code in a way that will compile on both Java 7 and
   * Java 8. If we include the {@code getAnnotatedBounds()} method then its return type means it
   * won't compile on Java 7, while if we don't include the method then the compiler will complain
   * that an abstract method is unimplemented. So instead we use a dynamic proxy to get an

     * TODO(cpovirk): use Object[] instead of E[] in the mainline? (The backport is different and
     * doesn't need this suppression, but we keep it to minimize diffs.) Generally be more clear
     * about when we have an Object[] vs. a Comparable[] or other array type in internalArray? If we
     * used Object[], we might be able to optimize toArray() to use clone() sometimes. (See
     * cl/592273615 and cl/592273683.)
     */

        Entry<?> entry = (Entry<?>) object;
        Object element = entry.getElement();
        int entryCount = entry.getCount();
        if (entryCount != 0) {
          // Safe as long as we never add a new entry, which we won't.
          // (Presumably it can still throw CCE/NPE but only if the underlying Multiset does.)
          @SuppressWarnings({"unchecked", "nullness"})

  // ...where "@JointlyNullable" is similar to @PolyNull but slightly different:
  //
  // - @PolyNull means "@Nullable or @Nonnull"
  //   (That would be unsound for an input Iterable<@Nullable Foo>. So, if we wanted to use
  //   @PolyNull, we would have to restrict this method to non-null <T>. But it has users who pass
  //   iterables with null elements.)
  //
  // - @JointlyNullable means "@Nullable or no annotation"
  @CheckForNull

          if (comparator == null) {
            // A sorted spliterator with no comparator is already using natural order.
            // (We could probably find a way to avoid rawtypes here if we wanted.)
            @SuppressWarnings({"unchecked", "rawtypes"})
            Comparator<? super E> naturalOrder =
                (Comparator<? super E>) Comparator.<Comparable>naturalOrder();

          // We're careful to put only K instances in.
          K[] sortedKs = (K[]) sortedKeys;
          Arrays.sort(sortedKs, comparator);
          Object[] sortedValues = new Object[size];

          // We might, somehow, be able to reorder values in-place.  But it doesn't seem like
          // there's a way around creating the separate sortedKeys array, and if we're allocating

   * {@code [1]} and {@code [1, 1]}).
   */
  // Note: 90% of the time we don't add type parameters or wildcards that serve only to "tweak" the
  // desired return type. However, *nested* generics introduce a special class of problems that we
  // think tip it over into being worthwhile.
  public static <T extends @Nullable Object, S extends T> Comparator<Iterable<S>> lexicographical(

    // Fail fast on a null. We throw NPE here because the contract of Executor states that it throws
    // NPE on null listener, so we propagate that contract up into the add method as well.
    checkNotNull(runnable, "Runnable was null.");
    checkNotNull(executor, "Executor was null.");

    // Lock while we check state. We must maintain the lock while adding the new pair so that

    // don't execute 'immediately'.  By checking isDone here we avoid that.
    // A corollary to all that is that we don't need to check isDone inside the loop because if we
    // get into the loop we know that we weren't done when we entered and therefore we aren't under
    // an obligation to execute 'immediately'.
    if (!isDone()) {
      Listener oldHead = listeners;