Bug 161222 Decoration label should be optional in Gantt Chart
It should not be mandatory to specify a decoration label for Gantt Charts, this can be left blank. Currently the UI and Engine enforce a data definition to be specified for it.
chart/org.eclipse.birt.chart.engine/src/org/eclipse/birt/chart/internal/datafeed/ResultSetWrapper.java
sExpression = ( (Query) elExpressions.get( i ) ).getDefinition( );
				iaColumnIndexes[i] = ( (Integer) htLookup.get( sExpression ) ).intValue( );
			}
		}
		catch ( Exception e )
		{
			throw new ChartException( ChartEnginePlugin.ID,
					ChartException.VALIDATION,
					"exception.base.orthogonal.null.datadefinition", 
					Messages.getResourceBundle( ) );
		}
		return new ResultSetDataSet( this, iaColumnIndexes, 0, getRowCount( ) );
	}
	/**
	 * Creates an instance of a resultset subset that uses references to
	 * dynamically compute a subset of the original resultset instance rather
	 * than duplicate a copy of the original resultset data content
	 * 
	 * @param sExpressionKey
	 *            A single expression column for which a resultset subset is
	 *            being requested
	 * 
	 * @return The resultset subset containing the requested column and all rows
	 *         of the resultset
	 */
	public ResultSetDataSet getSubset( String sExpressionKey )
	{
		return new ResultSetDataSet( this, new int[]{
			( (Integer) htLookup.get( sExpressionKey ) ).intValue( )
		}, 0, getRowCount( ) );