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
{
			GridData data = new GridData( );
			dataSourceLabel.setLayoutData( data );
		}
		availableDbObjectsTree = new Tree( tablescomposite, SWT.BORDER
				| SWT.MULTI );
		{
			GridData data = new GridData( GridData.FILL_BOTH );
			data.grabExcessHorizontalSpace = true;
			data.grabExcessVerticalSpace = true;
			data.heightHint = 150;
			availableDbObjectsTree.setLayoutData( data );
		}
		availableDbObjectsTree.addMouseListener( new MouseAdapter( ) {
			public void mouseDoubleClick( MouseEvent e )
			{
				populateEventData( e );
				insertText( (String) e.data );
			}
		} );
		availableDbObjectsTree.addSelectionListener( new SelectionAdapter( ) {
			public void widgetSelected( SelectionEvent event )
			{
				if ( event.widget.getClass( ) != null )
					handleAvailabeTreeSelection( );
			}
			private void handleAvailabeTreeSelection( )
			{
				TreeItem items[] = availableDbObjectsTree.getSelection( );
				for ( int i = 0; i < items.length; i++ )