Bug 148626 [Regression]Can't fetch value from the filter of table/chart which inherites data from container
Steps: 1. create a table and bind a dataset in it 2. create another table/chart in the table detail/table group header 3. switch to the Filter tab in property editor 4. create a filter and select value in "<select value...>" combo 5. an error popuped up, "The expression value can't be retrieved"
chart/org.eclipse.birt.chart.reportitem.ui/src/org/eclipse/birt/chart/reportitem/ui/ReportDataServiceProvider.java
ResultSetColumnHandle resultSetColumn = (ResultSetColumnHandle) iter.next( );
				ComputedColumn column = StructureFactory.newComputedColumn( handle,
						resultSetColumn.getColumnName( ) );
				column.setDataType( resultSetColumn.getDataType( ) );
				column.setExpression( DEUtil.getExpression( resultSetColumn ) );
				columnList.add( column );
			}
			return columnList;
		}
		return Collections.EMPTY_LIST;
	}
	/**
	 * Gets dataset from ReportItemHandle at first. If null, get dataset from
	 * its container.
	 * 
	 * @return direct dataset
	 */
	protected DataSetHandle getDataSetFromHandle( )
	{
		if ( itemHandle.getDataSet( ) != null )
		{
			return itemHandle.getDataSet( );
		}
		List datasetList = DEUtil.getDataSetList( itemHandle.getContainer( ) );
		if ( datasetList.size( ) > 0 )
		{
			return (DataSetHandle) datasetList.get( 0 );
		}
		return null;
	}