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
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( ); 
						}
						
						Object obj = oaTuple[iBaseColumnIndex];
						
						if ( obj instanceof CDateTime )
						{
							baseReference = (CDateTime) obj;
						}
						else if ( obj instanceof Calendar )
						{
							baseReference = new CDateTime( (Calendar) obj );
						}
						else if ( obj instanceof Date )
						{
							baseReference = new CDateTime( (Date) obj );
						}
						else
						{
							
							baseReference = new CDateTime( 0 );