Streams: Stream.reduce without an identity returns an Optional

The one-argument reduce has no identity value to fall back on for an empty stream, so it wraps its result in an Optional instead of returning the raw type directly.

Code

List<Integer> nums = List.of(3, 7, 2, 9, 4);
Optional<Integer> max = nums.stream().reduce(Integer::max);
System.out.println("Max via reduce: " + max.get());
Optional<Integer> maxEmpty = List.<Integer>of().stream().reduce(Integer::max);
System.out.println("Reduce on empty stream: " + maxEmpty);

Output

Max via reduce: 9
Reduce on empty stream: Optional.empty