Bug 121682 Exception throws when export data from table containing highlight/map.
Description: Exception throws when export data from attached report. Steps to reproduce: 1. I add a table which has a group, a highlight rule and a map rule in group row. 2. Preview the report attached. 3. Export the data in table. Expected result: Data are exported. Actual result: Exception in: ReportEngineService.getMetaData( )
engine/org.eclipse.birt.report.engine/src/org/eclipse/birt/report/engine/api/impl/DataExtractionTask.java
public void selectColumns( String[] columnNames )
	{
		selectedColumns = columnNames;
	}
	public IExtractionResults extract( ) throws EngineException
	{
		if( instanceId == null ) 
			return null;
		
		assert executionContext.getDataEngine() != null;
		DataEngine dataEngine = executionContext.getDataEngine().getDataEngine();
		
		ReportItemDesign rptItem = (ReportItemDesign) report
				.getReportItemByID( instanceId.getComponentID( ) );
		assert rptItem != null;
		
		IBaseQueryDefinition query = rptItem.getQuery();
		validateSelectedColumns( query );
		
		
		DataID dataId = instanceId.getDataID();
		InstanceID instId = instanceId;
		while( instId != null && dataId == null ){
			instId = instId.getParentID( );
			if( instId != null )
			{
				dataId = instId.getDataID();
			}
		}