private static final long serialVersionUID = 0;
  }

  /**
   * Returns a synchronized (thread-safe) {@code SetMultimap} backed by the specified multimap.
   *
   * <p>You must follow the warnings described in {@link #synchronizedMultimap}.
   *
   * <p>The returned multimap will be serializable if the specified multimap is serializable.
   *
   * @param multimap the multimap to be wrapped