Bug 145478 Unable "Select Value" in the Join data set's filter
Step to reproduce: 1.new a join data set(please use the attached file) 2.right click the dataset and click the Edit 3.go to the Filter pane and set a filer 4.click the list of Value1 Actual result: A warning pop up and cant select Value.
UI/org.eclipse.birt.report.designer.ui/src/org/eclipse/birt/report/designer/data/ui/util/DataSetProvider.java
return null;
	}
	
	/**
	 * This function should be called very carefully. Presently it is only
	 * called in DataSetEditorDialog#performCancel.
	 * 
	 * @param dataSet
	 * @param itemModel
	 */
	public void setModelOfDataSetHandle( DataSetHandle dataSet,
			DataSetViewData[] dsItemModel )
	{
		if ( dataSet == null || dsItemModel == null )
			return;
		updateModel( dataSet, dsItemModel );
		htColumns.put( dataSet, dsItemModel );
	}
	/**
	 * @param dataSet
	 * @return
	 * @throws BirtException
	 */
	public IQueryResults execute( DataSetHandle dataSet ) throws BirtException
	{
		return execute( dataSet, true, true, -1 );
	}
	
	/**
	 * execute query definition