Rewrite Optional.ofNullable(A).orElse(B) to requireNonNullElse(A, B)

[EnricSala]

Problem

Sometimes a nullable variable can be wrapped in an Optional simply to perform a null-or-else check.

In such cases it's simpler to use requireNonNullElse or requireNonNullElseGet from java.util.Objects.

Description of the proposed new feature

• Support a stylistic preference.
• Avoid a common gotcha, or potential problem.

I would like to rewrite the following code:

Optional.ofNullable(A).orElse(B);
Optional.ofNullable(A).orElseGet(() -> getB());

to:

requireNonNullElse(A, B);
requireNonNullElseGet(A, () -> getB());

Considerations

Could also consider the case Optional.of(A).orElse(B) which can be rewritten as just A, and similar for orElseGet.
EDIT: actually, Optional.of would already throw an exception if A was null, while replacing with just A could propagate the null further, so it should be replaced with requireNonNull(A).

Participation

• I am willing to submit a pull request to implement this improvement.

[Stephan202]

Nice one. The first Optional.ofNullable case can be added to this existing rule, provided that the Javadoc is tweaked a bit. Note that the same caveat around B possibly being null applies. (We might be able to partially mitigate this by applying a custom @Matches annotation 🤔.)

[Stephan202]

NB: I see I had this same rule in my private TODO list, followed by:

• requireNonNullElse(map.get(k), defaultValue) -> map.getOrDefault(k, defaultValue)

[Stephan202]

Another observation: the Optional.of rule has a reactive analog; from my TODO list:

• Mono.just(elem).defaultIfEmpty(elem2) -> Mono.just(elem)

Edit: though we may want to use a BugChecker to generalize this to any reactive expression that is known to be non-empty, such as flux.collect(..).

Edit 2: ah, but we already have NonEmptyMono for that. My local TODO list is outdated ;)

Edit 3: ah, but we documented that this specific case isn't covered yet 🙃,