txn.begin(new EmptyTxnContext());
PPusher.initialize();
final RefreshableDataGridColumnDescriptor<Data, Data, PHTML> descriptor = new RefreshableDataGridColumnDescriptor<Data, Data, PHTML>();
descriptor.setValueProvider(new IdentityValueProvider<Data>());
descriptor.setHeaderCellRenderer(new HeaderCellRenderer() {
@Override
public IsPWidget render() {
return new PLabel("The header");
}