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
protected ArrayList schemaList;
	 
	protected ArrayList tableList;
	
	private Connection jdbcConnection = null;
	private static String TABLE_ICON = "org.eclipse.birt.report.data.oda.jdbc.ui.editors.SQLDataSetEditorPage.TableIcon";
	private static String VIEW_ICON = "org.eclipse.birt.report.data.oda.jdbc.ui.editors.SQLDataSetEditorPage.ViewIcon";
	private static String PAGE_ICON = "org.eclipse.birt.report.data.oda.jdbc.ui.editors.SQLDataSetEditorPage.PageIcon";
	private static String SCHEMA_ICON = "org.eclipse.birt.report.data.oda.jdbc.ui.editors.SQLDataSetEditorPage.SchemaIcon";
	private static String DATABASE_ICON = "org.eclipse.birt.report.data.oda.jdbc.ui.editors.SQLDataSetEditorPage.DbIcon";
	private static String COLUMN_ICON = "org.eclipse.birt.report.data.oda.jdbc.ui.editors.SQLDataSetEditorPage.ColumnIcon";
	private static String DEFAULT_MESSAGE = JdbcPlugin.getResourceString( "dataset.new.query" );	
	
	static
	{
		try
		{	
			ImageRegistry reg = JFaceResources.getImageRegistry( );
			reg.put( TABLE_ICON,
					ImageDescriptor.createFromFile( JdbcPlugin.class,
							"icons/table.gif" ) );
			reg.put( VIEW_ICON,
					ImageDescriptor.createFromFile( JdbcPlugin.class,
							"icons/view.gif" ) );
			reg.put( PAGE_ICON,
					ImageDescriptor.createFromFile( JdbcPlugin.class,
							"icons/create_join_wizard.gif" ) );
			reg.put( SCHEMA_ICON,
					ImageDescriptor.createFromFile( JdbcPlugin.class,