* more convenient.
   *
   * <p>Builder instances can be reused - it is safe to call {@link #buildOrThrow} multiple times to
   * build multiple maps in series. Each map is a superset of the maps created before it.
   *
   * @since 2.0
   */
  public static class Builder<K, V> extends ImmutableMap.Builder<K, V> {
    private transient @Nullable Object[] keys;