Bug 161191 Null is inserted when drag columns to query text with ctrl key pressed
Description: Null is inserted when drag columns to query text with ctrl key pressed Steps to reproduce: 1. New a data source. 2. New a dataset. 3. Press and hold ctrl key, select OFFICECODE and CITY columns, drag to query text. Expected result: "CLASSICMODELS.OFFICES.OFFICECODE,CLASSICMODELS.OFFICES.CITY" is inserted in query text. Actual result: "null,CLASSICMODELS.OFFICES.OFFICECODE,CLASSICMODELS.OFFICES.CITY" is inserted
data/org.eclipse.birt.report.data.oda.jdbc.ui/src/org/eclipse/birt/report/data/oda/jdbc/ui/editors/SQLDataSetEditorPage.java
{
	
	private Image schemaImage, tableImage, viewImage, 
		    dataBaseImage, columnImage;
	
	private Document doc = null;
	private SourceViewer viewer = null;
	private TreeItem rootNode = null;
	private Text searchTxt = null;
	private ComboViewer filterComboViewer = null;
	private Combo schemaCombo = null;
	private Label schemaLabel = null;
	private Tree availableDbObjectsTree = null;
	private Button identifierQuoteStringCheckBox = null; 
	private TreeItem[] selectionMac = null;
	private boolean isSchemaSupported = false;
	private boolean expandDbObjectsTree = false;
    private IMetaDataProvider metaDataProvider = null;
    private JdbcSQLSourceViewerConfiguration sourceViewerConfiguration = null;
	private String cachedSearchTxt = "";
	private String formerQueryTxt = "";
	private String cachedDbType = "";
	private int cachedSchemaComboIndex = -1;
	private DataSourceDesign prevDataSourceDesign;
	private DataSetDesign dataSetDesign;