Constraint Validation

Question

I am using javax.validation.Validator and relevant classes for annotation based validation.

Configuration<?> configuration = Validation.byDefaultProvider().configure();   
ValidatorFactory factory = configuration.buildValidatorFactory();   
Validator validator = factory.getValidator(); 

Set<ConstraintViolation<ValidatableObject>> constraintViolations = validator.validate(o);   
for (ConstraintViolation<ValidatableObject> value : constraintViolations) {   
     List< Class< ? extends ConstraintValidator< ? extends Annotation,?>>> list = 
             value.getConstraintDescriptor().getConstraintValidatorClasses();  
}

I get a compilation error stating:

Type mismatch: cannot convert from List< Class< ? extends ConstraintValidator< capture#4-of ?,?>>> to List< Class< ? extends ConstraintValidator< ? extends Annotation,?>>>

What am I missing?