public final V forcePut(K key, V value) {
    throw new UnsupportedOperationException();
  }

  /**
   * Serialized type for all ImmutableBiMap instances. It captures the logical contents and they are
   * reconstructed using public factory methods. This ensures that the implementation types remain
   * as implementation details.
   *
   * <p>Since the bimap is immutable, ImmutableBiMap doesn't require special logic for keeping the