Grails validation dependent on other attributes

Question

What is the correct way to do something like this with grails:

class myDomainThing {
  String description
  MyOtherDomainThing otherThing

  static constraints = {
    description(nullable:if(otherThing))
    otherThing(nullable:if(description))
  }
}

So I either want there to be a link to the otherDomainThing or I want a String description.