private static final int DEFAULT_VALUES_PER_KEY = 2;

  @VisibleForTesting transient int expectedValuesPerKey = DEFAULT_VALUES_PER_KEY;

  /**
   * Creates a new, empty {@code HashMultimap} with the default initial capacities.
   *
   * <p>You may also consider the equivalent {@code
   * MultimapBuilder.hashKeys().hashSetValues().build()}, which provides more control over the
   * underlying data structure.
   */