Bug 141950 Selection of select value in data set filter is error
Details: Selection of select value in data set filter is error Step: 1.New a report design. 2.Create a sample datasource and dataset. 3.Switch to filter. 4.Select a value in expression. 5.Drop the list of the value1 and select <select value...> Actual result: No value is appear and pop up an error. It said that "An expression has not been set"
UI/org.eclipse.birt.report.designer.ui/src/org/eclipse/birt/report/designer/data/ui/util/DataSetProvider.java
if ( columns == null )
		{
			columns = new DataSetViewData[]{};
			updateModel( dataSet, columns );
			htColumns.put( dataSet, columns );
		}
		return columns;
	}
	/**
	 * @param dataSet
	 * @return
	 */
	private final DataSetViewData[] getCachedColumns( DataSetHandle dataSet )
	{
		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;