Hi gurus

I have trouble with binding Boolean property in association classes. Property is set to true if I check checkbox (good), but is null if checbox is not checked.

I know the problem with HTML checkbox. I know why is send "_fieldName" in params, but this "_fieldName" dont set my boolean property to false.

class Person{
   String title

   List<Group> groups = new ArrayList()
   static hasMany = [groups: Groups]    
}

class Group{
   String title
   Boolean isHidden

   static belongTo = Person
}

class PersonController{

   def form = {
      def person = new Person()
      person.groups.add( new Group() )    
      return ["person": person]
   }

   def handleForm = {
      def person = new Person( params )
      println person.groups[0]
   }
}

If I check checkbox:
[isHidden:on, title:a, _isHidden:]
println person.groups[0] //true

If I don check checkbox:
[title:a, _isHidden:]
println person.groups[0] //null

Thank a lot for help
Tom
I am sorry, I searched this web, but did not get actual info for my trouble.