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
switch ( unit.getValue( ) )
			{
				case GroupingUnitType.SECONDS :
					return Calendar.SECOND;
				case GroupingUnitType.MINUTES :
					return Calendar.MINUTE;
				case GroupingUnitType.HOURS :
					return Calendar.HOUR_OF_DAY;
				case GroupingUnitType.DAYS :
					return Calendar.DATE;
				case GroupingUnitType.WEEKS :
					return Calendar.WEEK_OF_YEAR;
				case GroupingUnitType.MONTHS :
					return Calendar.MONTH;
				case GroupingUnitType.YEARS :
					return Calendar.YEAR;
			}
		}
		return Calendar.MILLISECOND;
	}
	private void groupDateTime( List resultSet, int iBaseColumnIndex,
			String[] saExpressionKeys, int[] iaBreaks,
			CDateTime ndeBaseReference, long iGroupingInterval,
			GroupingUnitType groupingUnit, IAggregateFunction[] iafa )
			throws ChartException
	{
		final int iOrthogonalSeriesCount = saExpressionKeys.length;
		final int[] iaColumnIndexes = new int[iOrthogonalSeriesCount];
		for ( int i = 0; i < iOrthogonalSeriesCount; i++ )
		{