// Clear each collection, to make previously returned collections empty.
    for (Collection<V> collection : map.values()) {
      collection.clear();
    }
    map.clear();
    totalSize = 0;
  }

  // Views

  /**
   * {@inheritDoc}
   *
   * <p>The returned collection is not serializable.
   */
  @Override
  public Collection<V> get(@ParametricNullness K key) {

    // Clear each collection, to make previously returned collections empty.
    for (Collection<V> collection : map.values()) {
      collection.clear();
    }
    map.clear();
    totalSize = 0;
  }

  // Views

  /**
   * {@inheritDoc}
   *
   * <p>The returned collection is not serializable.
   */
  @Override
  public Collection<V> get(@ParametricNullness K key) {