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
Object[] oaTuple, oaSummarizedTuple = null;
			int iGroupIndex = 0, iLastGroupIndex = 0;
			boolean bFirst = true, bGroupBreak = false;
			double dBaseReference = baseReference.getValue( );
			List trashList = new ArrayList( );
			double dLastReference = dBaseReference;
			for ( int j = iStartIndex; j < iEndIndex; j++ )
			{
				oaTuple = (Object[]) resultSet.get( j );
				if ( oaTuple[iBaseColumnIndex] != null )
				{
					if ( iGroupingInterval == 0 )
					{
						if ( ( (Number) oaTuple[iBaseColumnIndex] ).doubleValue( ) != dLastReference )
						{
							iGroupIndex++;
						}
					}
					else
					{
						iGroupIndex = (int) Math.floor( Math.abs( ( ( (Number) oaTuple[iBaseColumnIndex] ).doubleValue( ) - dBaseReference )
								/ iGroupingInterval ) );
					}
					dLastReference = ( (Number) oaTuple[iBaseColumnIndex] ).doubleValue( );
				}
				else
				{
					if ( iGroupingInterval == 0 )
					{
						if ( !Double.isNaN( dLastReference ) )