When inconsistently invoking validateParameters() by passing an object and a method not defined on the object's type, an NPE in ValidatorImpl#validateParametersInContext() occurs:

ExecutableMetaData methodMetaData = beanMetaData.getMetaDataFor( validationContext.getExecutable() );
methodMetaData.assertCorrectnessOfMethodParameterConstraints();

We should throw a more meaningful exception in this case.