}

    @Override
    public @Nullable V computeIfPresent(
        K key, BiFunction<? super K, ? super @NonNull V, ? extends @Nullable V> remappingFunction) {
      throw new UnsupportedOperationException();
    }

    @Override
    public @Nullable V compute(
        K key,
        BiFunction<? super K, ? super @Nullable V, ? extends @Nullable V> remappingFunction) {

  @Override
  public @Nullable V computeIfPresent(
      K key, BiFunction<? super K, ? super V, ? extends @Nullable V> function) {
    checkNotNull(key);
    checkNotNull(function);
    return compute(key, (k, oldValue) -> (oldValue == null) ? null : function.apply(k, oldValue));
  }

  @Override
  public @Nullable V merge(
      K key, V newValue, BiFunction<? super V, ? super V, ? extends @Nullable V> function) {