[MODExt] MODx.grid.Grid usage

root is undefined

var root = this.getRoot(o), c = root.length, totalRecords = c, success = true; 

Quore.grid.Tagcategories = function(config) {
    config = config || {};
    Ext.applyIf(config,{
        id: 'quore-grid-tagcategories'
        ,url: Quore.config.connector_url
        ,autoDestroy: true
        ,baseParams: {action: 'mgr/tagcategories/getList'}
        ,fields: ['id','category_name','category_alias','menu']
        ,save_action: 'mgr/tagcategories/updateFromGrid'
        ,paging: true
        ,autosave: true
        ,remoteSort: true
        ,width: '95%'
        ,columns: [{
            header: 'ID'
            ,dataIndex: 'id'
            ,sortable: true
            ,width: 100
        },{
            header: 'Name'
            ,dataIndex: 'category_name'
            ,sortable: true
            ,width: 300
            ,editor: {xtype: 'textfield' ,allowBlank: true}
        },{
            header: 'Alias'
            ,dataIndex: 'category_alias'
            ,sortable: true
            ,width: 300
            ,editor: {xtype: 'textfield' ,allowBlank: true}
        }]
        ,tbar: [{
            text: 'Create Category'
            ,handler: this.createCategory
            ,scope: this
        },'-',{
            text: 'Refresh'
            ,handler: this.refresh
            ,scope: this
        }]
    });
    Quore.grid.Tagcategories.superclass.constructor.call(this,config)
};
Ext.extend(Quore.grid.Tagcategories,MODx.grid.Grid,{
    windows: {},
//edit and remove handlers,

    createCategory: function(btn,e) {
        if (!this.windows.createCategory) {
            this.windows.createCategory = MODx.load({
                xtype: 'quore-window-category-create'
                ,listeners: {
                    'success': {fn: function() {
                            this.refresh();
                            //console.log('added');
                        }, scope: this
                    }
                }
            });
        }
        this.windows.createCategory.show(e.target);
    }

});
Ext.reg('quore-grid-tagcategories',Quore.grid.Tagcategories);

Quore.window.CreateCategory = function(config) {
    config = config || {};
    Ext.applyIf(config,{
        title: 'Create Category'
        ,id: 'quore-tag-category-create'
        ,height: 200
        ,width: 500
        ,url: Quore.config.connector_url
        ,action: 'mgr/tagcategories/create'
        ,fields: [{
            xtype: 'textfield'
            ,fieldLabel: 'Name'
            ,name: 'name'
            ,id: 'quore-tag-category-name'
            ,width: 300
            ,allowBlank: false
        },{
            xtype: 'textfield'
            ,fieldLabel: 'Alias'
            ,name: 'alias'
            ,id: 'quore-tag-category-alias'
            ,width: 300
            ,allowBlank: false
        }]
    });
    Quore.window.CreateCategory.superclass.constructor.call(this,config);
};
Ext.extend(Quore.window.CreateCategory,MODx.Window);
Ext.reg('quore-window-category-create',Quore.window.CreateCategory);