Using nestedlist as an xtype throws the error Uncaught TypeError: Cannot call method 'getRootNode' of undefined

No matter what else is defined in it, xtype: 'nestedlist' will throw the error.


I was trying to implement this kitchensink nestedlist example as an xtype:

Code:
  var nestedList = new Ext.NestedList({
            fullscreen: true,          
            items: [{
                text: 'Option A',
                items: [{
                    text: 'Option A.1',
                    customAttribute: 123,
                    items: [{
                        text: 'Option A.1.a'
                    },{
                        text: 'Option A.1.b'
                    }]
                },{
                    text: 'Option A.2',
                    customAttribute: 389
                }]
            },{
                text: 'Option B',
                items: [{
                    text: 'Option B.1',
                    customAttribute: 233
                },{
                    text: 'Option B.2',
                    customAttribute: 2390
                }]
            },{
                text: 'Option C',
                items: [{
                    text: 'Option C.1',
                    customAttribute: 903
                },{
                    text: 'Option C.2',
                    customAttribute: 77
                }]
            }]        
        });