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
if(dataId == null)
			return null;
		
		DataSetID dataSetId = dataId.getDataSetID( );
		assert dataSetId != null;
		
		String queryResultName = dataSetId.getDataSetName( );
		
		if( resultMetaList == null )
		{
			resultMetaList = new ArrayList( );
		}
		else
		{
			resultMetaList.clear();
		}
		
		if ( queryResultName != null )
		{
			try
			{
				IQueryResults queryResults = dataEngine.getQueryResults( queryResultName );
				
				assert queryResults.getResultIterator() != null;
				
				ExtractionResults results = new ExtractionResults( queryResults.getResultIterator() 
						, selectedColumns, query.getRowExpressions() );
				resultMetaList.add( results.getResultMetaData() );
				return results;