Bug 135465 [smoke]An error occurred when new a casading Parameter
Description: An error occurred when new a casading Parameter Step to reproduce: 1.new a sample db data source and data set 2.New a cascading parameter group, named "gp1", 3.select the data set, then create two cascading parameters, one is row["customernumber"], named p1; the other is row["customername"] Actual result; error message occurred repeatly
UI/org.eclipse.birt.report.designer.ui/src/org/eclipse/birt/report/designer/ui/dialogs/CascadingParametersDialog.java
selection = new StructuredSelection( valueTable.getTable( )
					.getItem( index )
					.getData( ) );
		}
		else
		{
			selection = StructuredSelection.EMPTY;
		}
		valueTable.setSelection( selection );
	}
	private void refreshDataSets( )
	{
		String selectedDataSetName = dataSetsCombo.getText( );
		String[] oldList = dataSetsCombo.getItems( );
		String[] newDataSets = ChoiceSetFactory.getDataSets( );
		if ( !Arrays.asList( oldList ).equals( Arrays.asList( newDataSets ) ) )
		{
			dataSetsCombo.setItems( newDataSets );
			dataSetsCombo.setText( selectedDataSetName );
		}
	}
	private String[] getDataSets( )
	{
		return (String[]) DEUtil.getDataSets( ).toArray( new String[0] );
	}
	private DataSetHandle getDataSet( String name )
	{
		if ( name == null )
		{
			return null;