[flexcoders] How to enable the data grid editable if the data grid has no data

[loveewind]

If the data grid has no data, even the editable property is set 
as 'true' ,the column in data grid can not be editable.

For example,

<mx:DataGrid width="100%" editable="true" id="productGrid" 
height="100%" doubleClick="viewProduct()">
<mx:columns>
<mx:DataGridColumn headerText="Product Code" editable="true " 
dataField="productCode" />
</mx:columns>
</mx:DataGrid>

I want to edit the column 'Product Code' and input some text.
Has anyone such experience?

Thanks