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 void refreshPage( )
	{
		
		DataSourceDesign curDataSourceDesign = this.getDataSetDesign( )
				.getDataSourceDesign( );
		if ( curDataSourceDesign != prevDataSourceDesign )
		{
			RemoveAllAvailableDbObjects( );
			resetJdbcInfo( curDataSourceDesign );
			enableSchemaComponent( isSchemaSupported );
			setRootElement( );
			sourceViewerConfiguration.getContentAssistProcessor( )
					.setDataSourceHandle( curDataSourceDesign );
			populateAvailableDbObjects( );
			prevDataSourceDesign = curDataSourceDesign;
		}
	}	
	
	/**
	 * 
	 */
	private void addFetchDbObjectListener( )
	{
		availableDbObjectsTree.addListener( SWT.Expand, new Listener( ) {
			/*
			 * @see org.eclipse.swt.widgets.Listener#handleEvent(org.eclipse.swt.widgets.Event)
			 */
			public void handleEvent( final Event event )
			{