Grails : Problems with Lazy List - grails

Question

I have a web page that allows the user to enter data which will form a Master / Detail relationship when stored to my database. I submit the data to a Grails controller that binds the data in to a Command Object. As I do not know how many "detail" rows will be submitted, I am attempting to use a Lazy List to bind the detail data to. I am failing spectacularly.
My command object looks like :
String title
List testItems = LazyList.decorate(new ArrayList(),
FactoryUtils.instantiateFactory(VocabQuestion.class));
When I submit the form I get the following exception :
| Error 2013-06-04 22:42:54,068 [http-bio-8080-exec-4] ERROR errors.GrailsExceptionResolver - MissingMethodException occurred when processing request: [POST] /*****/vocabulary/save - parameters:
testItems[1].question: Q2
title: Test
testItems[0].answer: A1
testItems[0].question: Q1
testItems[0].vocabulary_test_id:
testItems[1].answer: A2
create: Create
No signature of method: vocabularytest.TestCreationCommand.propertyMissing() is applicable for argument types: () values: []
Possible solutions: propertyMissing(java.lang.String). Stacktrace follows:
Message: No signature of method: vocabularytest.TestCreationCommand.propertyMissing() is applicable for argument types: () values: []
Possible solutions: propertyMissing(java.lang.String)
Line | Method
->> 102 | <init> in vocabularytest.TestCreationCommand
This exception happens very early on in the objects lifecycle, presumeably as Grails tries to bind the data to it.
If I define my Command Object as :
String title
List testItems = [new VocabQuestion()]
and only submit 1 detail record from the form, then everything works as expected.
Where am I going wrong?
EDIT
My VocabQuestion domain class is
package vocabularytest
class VocabQuestion {
static constraints = {
}
static belongsTo = [vocabularyTest: VocabularyTest]
String question
String answer
}

Answer 1

I found an answer ( might not be THE answer but it works )
I used the LazyList syntax that is native in later Groovy versions as follows.
List testItems = [].withLazyDefault {new VocabQuestion()}