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
/**
	 * 
	 * @return
	 */
	private DataSetDesign getDataSetDesign( )
	{
		if ( dataSetDesign == null )
			dataSetDesign = this.getInitializationDesign( );
		return dataSetDesign;
	}
	
	/**
	 * populate shema list if the schema is supported
	 * 
	 */
	protected void populateSchemaList( )
	{
		if ( rootNode != null )
		{
			removeTreeItem( rootNode );
		}
		getAvailableSchema( );
		
		if ( schemaCombo.getItemCount( ) < 1 )
		{
			schemaCombo.add( JdbcPlugin.getResourceString( "tablepage.text.All" ) );
			schemaCombo.select( 0 );
			if ( schemaList != null )
			{