Bug 147263 Data can't be retrieved for extended item
Steps to reproduce: 1.Add a table in library 2.New a report, extend lib.table 3.Add a filter on table, choose "select value" Expected result: Available value will be listed Actual result: Error: The expression's value can not be retrieved. The DataSetHandle shouldn't be null.
data/org.eclipse.birt.report.data.adapter/src/org/eclipse/birt/report/data/adapter/impl/DataRequestSessionImpl.java
{
		dataEngine.closeDataSource( dataSourceName );
	}
	/*
	 * @see org.eclipse.birt.report.data.adaptor.impl.IDataRequestSession#getModelAdaptor()
	 */
	public IModelAdapter getModelAdaptor( )
	{
		return modelAdaptor;
	}
	/*
	 * @see org.eclipse.birt.report.data.adaptor.impl.IDataRequestSession#shutdown()
	 */
	public void shutdown( )
	{
		dataEngine.shutdown( );
		dataEngine = null;
	}
	/**
	 * get the distinct value of query
	 * @param dataSet
	 * @param inputParamBindings
	 * @param columnBindings
	 * @param boundColumnName
	 * @return
	 * @throws BirtException
	 */
	private IQueryResults getGroupingQueryResults( DataSetHandle dataSet,
			Iterator inputParamBindings, Iterator columnBindings,
			String boundColumnName ) throws BirtException