return new UnmodifiableTable<>(table);
  }

  private static class UnmodifiableTable<
          R extends @Nullable Object, C extends @Nullable Object, V extends @Nullable Object>
      extends ForwardingTable<R, C, V> implements Serializable {
    final Table<? extends R, ? extends C, ? extends V> delegate;

    UnmodifiableTable(Table<? extends R, ? extends C, ? extends V> delegate) {