return new FunctionComposition<>(g, f);
  }

  private static final class FunctionComposition<
          A extends @Nullable Object, B extends @Nullable Object, C extends @Nullable Object>
      implements Function<A, C>, Serializable {
    private final Function<B, C> g;
    private final Function<A, ? extends B> f;

    FunctionComposition(Function<B, C> g, Function<A, ? extends B> f) {