WebFlux AbstractView does not update BindingResult for resolved async attributes

[dsyer]

In ViewResolutionResultHandler.handleResult() we have

	updateBindingContext(result.getBindingContext(), exchange);

	return viewsMono.flatMap(views -> render(views, model.asMap(), exchange));

so the binding context is updated before rendering starts. Later as part of rendering, AbstractView calls resolveAsyncAttributes to resolve Mono and Flux attributes in the model to concrete values, but the BindingResult for each of those attributes are not updated accordingly.

This means that any View that inspects the BindingResult to find out about field errors etc. will break, e.g.

Caused by: org.springframework.beans.NotReadablePropertyException: Invalid property 'firstName' of bean class [reactor.core.publisher.MonoOnAssembly]: Bean property 'firstName' is not readable or has an invalid getter method: Does the return type of the getter match the parameter type of the setter?
    at org.springframework.beans.AbstractNestablePropertyAccessor.getPropertyValue(AbstractNestablePropertyAccessor.java:622)
    at org.springframework.beans.AbstractNestablePropertyAccessor.getPropertyValue(AbstractNestablePropertyAccessor.java:612)
    at org.springframework.validation.AbstractPropertyBindingResult.getActualFieldValue(AbstractPropertyBindingResult.java:104)
    at org.springframework.validation.AbstractBindingResult.getFieldValue(AbstractBindingResult.java:228)
    at org.springframework.web.reactive.result.view.BindStatus.<init>(BindStatus.java:127)
    at org.springframework.web.reactive.result.view.RequestContext.getBindStatus(RequestContext.java:442)
    at org.thymeleaf.spring5.context.webflux.SpringWebFluxThymeleafRequestContext.getBindStatus(SpringWebFluxThymeleafRequestContext.java:227)
    at org.thymeleaf.spring5.util.FieldUtils.getBindStatusFromParsedExpression(FieldUtils.java:306)
    at org.thymeleaf.spring5.util.FieldUtils.getBindStatus(FieldUtils.java:253)
...