NPE in ErrorsMethodArgumentResolver [SPR-16187]

[spring-projects-issues]

Rossen Stoyanchev opened SPR-16187 and commented

This is based on a Spring Boot ticket spring-projects/spring-boot#10950. The specific use case that led to the NPE is a BindingResult argument after an @RequestBody which is not supported.

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Affects: 5.0.1

Referenced from: commits ff97eaf

[spring-projects-issues]

Rossen Stoyanchev commented

About the combination of @RequestBody + BindingResult, since on the WebFlux side controller methods can declare a request body argument with a reactive type wrapper, they also have natural access to error signals such as WebExchangeBindException via onError operators.

We could consider support BindingResult still as a convenience but that works only for Mono and not for Flux since the Flux is yet to be consumed, and even with a Mono<BindingResult> you'd have be careful to use the Flux for the body first and then check the Mono for the errors. It makes no sense to represent errors this way.

In short the advice is to use onError operators for access to errors inside the controller method and this applies to @RequestBody, @RequestPart, and HttpEntity arguments. I've added an error message to that effect in the resolver.