Topic/validator options

I ran into a case at work where using:
    validate("column-name").isUUID( { onlyNotNull: true } );
would reject an update on a loaded model with "'column-name' must be a valid UUID got null".

I don't have 'make test' working at home yet, but the logic change to enable the option was simple enough.  Letting 'onlyDefined === false' override onlyNotNull in case of a conflict seemed best.