Add ResponseEntity.ofNullable() to deal with non-Optional nullable objects

[davefranken-ah]

Affects: All versions

---

Context
I like that <T> ResponseEntity<T> ResponseEntity.of(Optional<T> body) gives a 200 OK with a body if it is present inside the optional and a 404 for an empty Optional.

Problem
However, sometimes you cannot or do not want to deal with Optional (for instance when using Kotlin) but still want to have a useful method like this.

Current workaround
The current workaround would be to just wrap it inside an Optional:
ResponseEntity.of(Optional.ofNullable(entity)) but this is pretty ugly and still creates an extra intermediate Optional object.

Proposal
My proposal would be to add a method:
<T> ResponseEntity<T> ResponseEntity.ofNullable(T body) which can be used by both Java and Kotlin to turn a nullable object into a 200 OK with body or 404.

The implementation would be pretty straightforward:

public static <T> ResponseEntity<T> ofNullable(T body) {
  if (body == null) {
    return notFound().build();
  }
  return ResponseEntity.ok(body);
}

[sdeleuze]

The use case seems valid to me, and I have don't have a better proposal for the name, we should just make sure to annotate correctly the parameter:

public static <T> ResponseEntity<T> ofNullable(@Nullable T body) {
  if (body == null) {
    return notFound().build();
  }
  return ResponseEntity.ok(body);
}

@poutsma @rstoyanchev Are you ok to introduce this variant?

[poutsma]

Sounds good to me.