Spring *ExceptionHandler not working with valiktor-spring-boot-starter

[dragneelfps]

Expected Behavior

ConstraintViolationException are automatically handled by ReactiveConstraintViolationExceptionHandler

Actual Behavior

ConstraintViolationException are handled by ExceptionHandlingWebHandler

Steps to Reproduce the Problem

1. Use spring kofu setup
2. Add org.valiktor:valiktor-spring-boot-starter:0.12.0 to deps.
3. Send request which throws ConstraintViolationException

PS C:\Users\srawa> Invoke-RestMethod "http://localhost:8000/api/user" -Body $User2 -Method POST -ContentType "application/json" | ConvertTo-Json

Invoke-RestMethod: {"timestamp":"2020-07-19T14:17:47.153+00:00","path":"/api/user","status":500,"error":"Internal Server Error","message":"","requestId":"64027368-1","exception":"org.valiktor.ConstraintViolationException"}

Server logs:

2020-07-19 19:47:47.166 ERROR 13776 --- [ctor-http-nio-2] a.w.r.e.AbstractErrorWebExceptionHandler : [64027368-1]  500 Server Error for HTTP POST "/api/user"

org.valiktor.ConstraintViolationException: null
	at io.nooblabs.eventmanagerbackend.User.validate(EventmanagerBackendApplication.kt:62) ~[main/:na]
	Suppressed: reactor.core.publisher.FluxOnAssembly$OnAssemblyException: 
Error has been observed at the following site(s):
	|_ checkpoint ⇢ HTTP POST "/api/user" [ExceptionHandlingWebHandler]
Stack trace:

Example Code or Link to a Project

val app = reactiveWebApplication {
    beans {
        bean<UserHandler>()
        bean(::routes)
    }
    webFlux {
        port = if (profiles.contains("test")) 8081 else 8000
        codecs {
            string()
            jackson()
        }
    }
}

data class User(
        val login: String,
        val name: String
) {

    fun validate(): User {
        _validate(this) {
            validate(User::login)
                    .isNotBlank()
                    .hasSize(min = 4, max = 8)
            validate(User::name)
                    .isNotBlank()
                    .hasSize(max = 32)
        }
        return this
    }
}

class UserHandler {
    suspend fun createApi(request: ServerRequest): ServerResponse {
        return request.awaitBody<User>()
                .validate()
                .let { user -> ok().bodyValueAndAwait(user) }
    }
}

fun routes(userHandler: UserHandler) = coRouter {
    POST("/api/user", userHandler::createApi)
}


fun main() {
    app.run()
}

Environment

• Valiktor version: 0.12.0
• JDK/JRE version: adopt-openj9-14.0.1
• Platform/OS: Win 10

[alc0der]

For me this only happens when invoking API from JUnit using @WebFluxTest; it works with @SpringBootTest.
I've tried to inject Beans for ValiktorExceptionHandler and ReactiveConstraintViolationExceptionHandler, but it made things worse.