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
return getDataSetMetaData( this.sessionContext.getModuleHandle( )
				.findDataSet( dataSetName ), useCache );
	}
	/*
	 * @see org.eclipse.birt.report.data.adaptor.api.DataRequestSession#getDataSetMetaData(org.eclipse.birt.report.model.api.DataSetHandle,
	 *      boolean)
	 */
	public IResultMetaData getDataSetMetaData( DataSetHandle dataSetHandle,
			boolean useCache ) throws BirtException
	{
		return new DataSetMetaDataHelper( this.dataEngine,
				this.modelAdaptor,
				this.sessionContext.getModuleHandle( ) ).getDataSetMetaData( dataSetHandle,
				useCache );
	}
	/*
	 * @see org.eclipse.birt.report.data.adapter.api.DataRequestSession#getColumnValueSet(org.eclipse.birt.report.model.api.DataSetHandle,
	 *      java.util.Iterator, java.util.Iterator, java.lang.String)
	 */
	public Collection getColumnValueSet( DataSetHandle dataSet,
			Iterator inputParamBindings, Iterator columnBindings,
			String boundColumnName ) throws BirtException
	{
		return getColumnValueSet( dataSet,
				inputParamBindings,
				columnBindings,
				boundColumnName,
				null );
	}