Grails validation error from service method

Question

I have a method in a service class that creates an object:

def createContent (fileName, description) {

    def content = new Content(
        fileName:fileName,
        description:description,
    ).save()
}

Neither of those properties are nullable. How can I pass the validation errors back to be displayed? I've tried flash.message and render, both of which don't work from within service classes. I also tried .save(failOnError:true) which displayed a long list of errors.