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
/ iGroupingInterval ) );
					}
					lastReference = (CDateTime) dCurrentValue.clone( );
				}
				else
				{
					
					CDateTime dCurrentValue = new CDateTime( 0 );
					if ( iGroupingInterval == 0 )
					{
						if ( !lastReference.equals( dCurrentValue ) )
						{
							iGroupIndex++;
						}
					}
					else
					{
						
						dCurrentValue.clearBelow( cunit );
						double diff = CDateTime.computeDifference( dCurrentValue,
								baseReference,
								cunit,
								true );
						iGroupIndex = (int) Math.floor( Math.abs( diff
								/ iGroupingInterval ) );
					}
					lastReference = (CDateTime) dCurrentValue.clone( );
				}
				if ( !bFirst )
				{