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
NumberDataElement ndeBaseReference, long iGroupingInterval,
			IAggregateFunction[] iafa ) throws ChartException
	{
		final int iOrthogonalSeriesCount = saExpressionKeys.length;
		final int[] iaColumnIndexes = new int[iOrthogonalSeriesCount];
		for ( int i = 0; i < iOrthogonalSeriesCount; i++ )
		{
			iaColumnIndexes[i] = ( (Integer) htLookup.get( saExpressionKeys[i] ) ).intValue( );
		}
		int iStartIndex = 0, iEndIndex;
		int totalGroupCount = iaBreaks == null ? 1 : ( iaBreaks.length + 1 );
		int totalRowCount = resultSet.size( );
		for ( int k = 0; k < totalGroupCount; k++ )
		{
			if ( k == totalGroupCount - 1 )
			{
				iEndIndex = totalRowCount;
			}
			else
			{
				iEndIndex = iaBreaks[k];
			}
			NumberDataElement baseReference = ndeBaseReference;
			if ( baseReference == null )
			{
				
				Number obj = (Number) ( (Object[]) resultSet.get( iStartIndex ) )[iBaseColumnIndex];
				baseReference = NumberDataElementImpl.create( obj == null ? 0
						: obj.doubleValue( ) );
			}