BAF - step 4, lazy loading the tree?

I’m currently working through this example in the book. Yes, I have looked at backdraft however, my question concerns some of the sample code for lazy loading the dijit.Tree.

I had most of this working under Dojo 1.7.2 but as soon as I added the tree components, it fell apart. Currently getting an error in Firebug with respect to the LazyTreeStore.js file…

args.root is undefined
this._idToItem[args.root.id] = args.root;

Not sure where this is coming from. If I set some breakpoints and step into it, I find that args is set to “obe.test.data.MockNavigatorDataBuilder” which seems to be correct except that it comes in as a string and not an object.

If someone could point me in the right direction, that would be much appreciated.

Thanks