ReOrder ListGrid with DataSource

[immobilia]

Hy, in a ListGrid, on onRecordDrop() i try to :
* update all records on ListGrid
* fetch ListGrid

It's working, but after the final fecth, if i will use again my grid records, i catch this error :

Uncaught JavaScript exception [com.google.gwt.dev.shell.HostedModeException: Expected primitive type int; actual value was undefined

On line : for( ListGridRecord lgr : countryGrid.getRecords() ) {
At method : countryGrid.getRecords()

Trace :
** First Pass ReOrder by Drag Drop ** :

RecordDropHandler event : An event type
countryGrid != NULL
countryGridgetRecords() != NULL

** Second Pass ReOrder by Drag Drop ** :

RecordDropHandler event : An event type
countryGrid != NULL
Uncaught JavaScript exception [com.google.gwt.dev.shell.HostedModeException: Expected primitive type int; actual value was undefined

	final ListGrid countryGrid = new ListGrid();  

        countryGrid.setDataSource(countryDS); 
        countryGrid.setAutoFetchData(true); 

        ....

        countryGrid.addRecordDropHandler(new RecordDropHandler() {

			@Override
			public void onRecordDrop(RecordDropEvent event) {

				System.out.println("RecordDropHandler event : " + event);
				
				if( countryGrid != null )
					System.out.println("countryGrid != NULL");
				if( countryGrid.getRecords() != null )
					System.out.println("countryGridgetRecords() != NULL");
				
				for( ListGridRecord lgr : countryGrid.getRecords() ) {
					// ReOrder by setAttribute
//					lgr.setAttribute("orderId", newOrder);
					
					countryGrid.updateData(lgr);
				}
				
				countryGrid.invalidateCache();
				countryGrid.fetchData();
				
			}
        	
        });

The last fetch should not refresh ListGrid cache ?

If i comment invalidateCache(), i haven't this error, but no ListGrid visual refresh.