*
   * <pre>{@code
   * public static final ImmutableMultiset<Bean> BEANS =
   *     new ImmutableMultiset.Builder<Bean>()
   *         .addCopies(Bean.COCOA, 4)
   *         .addCopies(Bean.GARDEN, 6)
   *         .addCopies(Bean.RED, 8)
   *         .addCopies(Bean.BLACK_EYED, 10)
   *         .build();
   * }</pre>
   *

    @Override
    @CheckForNull
    public E getNext() {
      return null;
    }
  }

  /** Marker interface for {@link InternalEntry} implementations for strong values. */
  interface StrongValueEntry<K, V, E extends InternalEntry<K, V, E>>
      extends InternalEntry<K, V, E> {}

  /** Marker interface for {@link InternalEntry} implementations for weak values. */

   * <p>If a task is {@linkplain Thread#interrupt interrupted} while a task is running:
   *
   * <ol>
   *   <li>execution will not stop until the task queue is empty.
   *   <li>tasks will begin execution with the thread marked as not interrupted - any interruption
   *       applies only to the task that was running at the point of interruption.
   *   <li>if the thread was interrupted before the SequentialExecutor's worker begins execution,

  // Timed Get
  // There are a few design constraints to consider
  // * We want to be responsive to small timeouts, unpark() has non trivial latency overheads (I
  //   have observed 12 micros on 64-bit linux systems to wake up a parked thread). So if the
  //   timeout is small we shouldn't park(). This needs to be traded off with the cpu overhead of
  //   spinning, so we use SPIN_THRESHOLD_NANOS which is what AbstractQueuedSynchronizer uses for

   *
   * <pre>{@code
   * public static final ImmutableMultiset<Bean> BEANS =
   *     new ImmutableMultiset.Builder<Bean>()
   *         .addCopies(Bean.COCOA, 4)
   *         .addCopies(Bean.GARDEN, 6)
   *         .addCopies(Bean.RED, 8)
   *         .addCopies(Bean.BLACK_EYED, 10)
   *         .build();
   * }</pre>
   *

   * <pre>{@code
   * public static final ImmutableSortedMultiset<Bean> BEANS =
   *     new ImmutableSortedMultiset.Builder<Bean>(colorComparator())
   *         .addCopies(Bean.COCOA, 4)
   *         .addCopies(Bean.GARDEN, 6)
   *         .addCopies(Bean.RED, 8)
   *         .addCopies(Bean.BLACK_EYED, 10)
   *         .build();
   * }</pre>
   *

   * <pre>{@code
   * public static final ImmutableSortedMultiset<Bean> BEANS =
   *     new ImmutableSortedMultiset.Builder<Bean>(colorComparator())
   *         .addCopies(Bean.COCOA, 4)
   *         .addCopies(Bean.GARDEN, 6)
   *         .addCopies(Bean.RED, 8)
   *         .addCopies(Bean.BLACK_EYED, 10)
   *         .build();
   * }</pre>
   *