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/ResultSetDataSet.java
if ( listMode )
		{
			return listDataType;
		}
		if ( iaColumnIndexes.length == 1 )
		{
			return rsw.getColumnDataType( iaColumnIndexes[0] );
		}
		return IConstants.UNDEFINED;
	}
	/*
	 * (non-Javadoc)
	 * 
	 * @see org.eclipse.birt.chart.datafeed.IResultSetDataSet#getColumnCount()
	 */
	public int getColumnCount( )
	{
		return iColumnCount;
	}
	/*
	 * (non-Javadoc)
	 * 
	 * @see org.eclipse.birt.chart.datafeed.IResultSetDataSet#getSize()
	 */
	public long getSize( )
	{
		return lEndRow - lStartRow;
	}
}