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
if ( iGroupCounter > iGroupingInterval )
					{
						iGroupIndex++;
					}
				}
				if ( !bFirst )
				{
					bGroupBreak = ( iLastGroupIndex != iGroupIndex );
				}
				if ( bGroupBreak )
				{
					
					iGroupCounter = 0;
				}
				if ( bGroupBreak || bFirst )
				{
					if ( oaSummarizedTuple != null ) 
					{
						for ( int i = 0; i < iOrthogonalSeriesCount; i++ )
						{
							oaSummarizedTuple[iaColumnIndexes[i]] = iafa[i].getAggregatedValue( );
							iafa[i].initialize( ); 
						}
						
						baseReference = ChartUtil.stringValue( oaTuple[iBaseColumnIndex] );
						iGroupIndex = 0;
					}
					else
					{