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
{
							iGroupIndex++;
						}
					}
					else
					{
						
						iGroupIndex = (int) Math.floor( Math.abs( dBaseReference
								/ iGroupingInterval ) );
					}
					dLastReference = Double.NaN;
				}
				if ( !bFirst )
				{
					bGroupBreak = ( iLastGroupIndex != iGroupIndex );
				}
				if ( bGroupBreak || bFirst )
				{
					if ( oaSummarizedTuple != null ) 
					{
						for ( int i = 0; i < iOrthogonalSeriesCount; i++ )
						{
							oaSummarizedTuple[iaColumnIndexes[i]] = iafa[i].getAggregatedValue( );
							iafa[i].initialize( ); 
						}
						
						Number obj = (Number) oaTuple[iBaseColumnIndex];
						baseReference = NumberDataElementImpl.create( obj == null ? 0
								: obj.doubleValue( ) );
						dBaseReference = baseReference.getValue( );