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
return iC;
		}
		else if ( a instanceof Number )
		{
			final double d1 = ( (Number) a ).doubleValue( );
			final double d2 = ( (Number) b ).doubleValue( );
			return ( d1 == d2 ) ? 0 : ( d1 < d2 ) ? -1 : 1;
		}
		else if ( a instanceof java.util.Date )
		{
			final long d1 = ( (java.util.Date) a ).getTime( );
			final long d2 = ( (java.util.Date) b ).getTime( );
			return ( d1 == d2 ) ? 0 : ( d1 < d2 ) ? -1 : 1;
		}
		else if ( a instanceof Calendar )
		{
			final long d1 = ( (Calendar) a ).getTime( ).getTime( );
			final long d2 = ( (Calendar) b ).getTime( ).getTime( );
			return ( d1 == d2 ) ? 0 : ( d1 < d2 ) ? -1 : 1;
		}
		else
		
		{
			return compareObjects( a.toString( ), b.toString( ) );
		}
	}
	/**
	 * GroupingComparator
	 */
	static final class GroupingSorter implements Comparator