Dynamically add fieldset to sencha FormPanel

add_fieldset.js

App.views.creditCardForm.items.items[0].up('form').insert(1, {
            xtype: 'fieldset',
            id: 'customerInfoFormFieldset',
            title: 'Name and Address Details',
            instructions: 'Please enter your name and address.',
            defaults: {
                xtype: 'textfield',
                labelAlign: 'left',
                labelWidth: '40%',
                required: false,
                useClearIcon: true,
                autoCapitalize : false
            },
            items: [
                {
                    name : 'name',
                    label: 'Name',
                    autoCapitalize : true
                },
                {
                    xtype: 'App.views.ErrorField',
                    fieldname: 'name'
                },
                {
                    name : 'address',
                    label: 'Address'
                },
                {
                    xtype: 'App.views.ErrorField',
                    fieldname: 'address'
                },
                {
                    name : 'city',
                    label: 'City',
                    autoCapitalize : true
                },
                {
                    xtype: 'App.views.ErrorField',
                    fieldname: 'city'
                },
                {
                    name : 'state',
                    label: 'State',
                    autoCapitalize : true
                },
                {
                    xtype: 'App.views.ErrorField',
                    fieldname: 'state'
                },
                {
                    name : 'zip',
                    label: 'Zip',
                },
                {
                    xtype: 'App.views.ErrorField',
                    fieldname: 'zip'
                }
            ]
        }
);