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
{
			final Object[] oaTuple1 = (Object[]) o1;
			final Object[] oaTuple2 = (Object[]) o2;
			final Object oC1 = oaTuple1[iSortIndex];
			final Object oC2 = oaTuple2[iSortIndex];
			if ( oC1 == null && oC2 == null )
			{
				return 0;
			}
			if ( oC1 == null && oC2 != null )
			{
				return ascending ? -1 : 1;
			}
			if ( oC1 != null && oC2 == null )
			{
				return ascending ? 1 : -1;
			}
			int ct;
			if ( oC1 instanceof String )
			{
				ct = collator.compare( oC1.toString( ), oC2.toString( ) );
			}
			else
			{
				ct = ( (Comparable) oC1 ).compareTo( oC2 );
			}
			return ascending ? ct : -ct;
		}
	}
}