Optional configuration parameter validation problem in 0.90-rc5

[lehcim]

After swtiching to version 0.90-rc5, my server failed to load its configuration with the following error message :

Exception in thread "main" javax.validation.UnexpectedTypeException: HV000186: 
The constraint of type 'javax.validation.constraints.NotNull' defined on 'client.userAgent' 
has multiple matching constraint validators which is due to an additional value handler of type 
'io.dropwizard.validation.valuehandling.OptionalValidatedValueUnwrapper'. 
It is unclear which value needs validating. Clarify configuration via @UnwrapValidatedValue.

The configuration field which trigger the exception is a dropwizard HttpClientConfiguration with a @Valid annotation:

public class PetConfiguration extends Configuration {
    @Valid    // remove this annotation to avoid HV000186
    public HttpClientConfiguration client ;
}

The problem is caused by the annotation @NotNull on the property userAgent in class HttpClientConfiguration. It can be reproduced with a simple String parameter, like this :

public class PetConfiguration extends Configuration {
    @NotNull
    @Valid    // remove this annotation to avoid HV000186 
    public Optional<String> foo = Optional.absent() ;
}

Everything is fine with the two configurations classes above using 0.90-rc4, I think it's a 0.90-rc5 regression, but I don't known the cause yet : to my knowledge, there was no change on HttpClientConfiguration.userAgent between rc4 and rc5 ...