Checking a group of fields in a grails domain object

I have a command object that captures a feedback form with 3 text areas.

class FeedbackCommand {
    String textarea1
    String textarea2
    String textarea3
    String username 

    static constraints = {
        textarea1(nullable:true, blank:true)            
        textarea2(nullable:true, blank:true)            
        textarea3(nullable:true, blank:true)            
        username(nullable:false, blank:false)
    }
}    

I would like to make sure that at least ONE of the text fields is full.

I came up with the addition of a fake field to the "restriction" field, and then performed a bunch of object checks in the custom validator for that field. If, after examining myself, I don’t find what I want, I make a mistake.

Now I am doing this:

class FeedbackCommand {
    String textarea1
    String textarea2
    String textarea3
    boolean atLeastOne = true
    String username 

    static constraints = {
        textarea1(nullable:true, blank:true)            
        textarea2(nullable:true, blank:true)            
        textarea3(nullable:true, blank:true) 
        atLeastOne(validator: { boolean b, FeedbackCommand form, Errors err ->
          if (b) {
            if ( (form.textarea1==null || form.textarea1?.isAllWhitespace()) &&
                 (form.textarea2==null || form.textarea2?.isAllWhitespace()) &&
                 (form.textarea3==null || form.textarea3?.isAllWhitespace()))
            {
                // They havent provided ANY feedback. Throw an error
                err.rejectValue("atLeastOne", "no.feedback")
                return false
            }
          }
          return true             
        })           
        username(nullable:false, blank:false)
    }
}

Is there a better way

• check related / group of fields (at least one cannot be empty, 2 must have values, etc.)?
• a more attractive way of expressing "at least one must be null / blank" rather than my heavy if-statement block?

thank