Grails testing a failing domain save in service

I've a Grails (3+) service where a domain object is retrieved from the DB, modified , and then updated in the DB.

class MyService {
    def modifyObject(String uuid) {
        def md = MyDomain.findByUuid(uuid)
        md.someField = true
        if (!md.save()){ 
            throw new MyException()
        }
    }
}

Now I need to test this service method with a negative test, to be sure that the exception is thrown. But I can't figure out how to force a failing save in the service method.

@TestFor(MyService)
@Mock(MyDomain)
class MyServiceSpec extends Specification {

    void "test An exceptionl situation was found"() {
        given: "An uuid"
            def md = new MyDomain(uuid: "123")
            md.save(failOnError: true)

        when: "service is called"
            service.modifyObject("123")

        then: "An exception is thrown"
            thrown MyException
    }
}

Obviously, re-defining the service method in a more functional way (the object is passed directly to the method, modified and returned without save .e.g MyDomain modifyObject(MyDomain md)) will be a good solution since I could create an invalid ad hoc object outside or even invalidate it after the method execution.

But the question is: "is there a way to test the service code as is?"