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
	 */
	public Iterator iterator( )
	{
		if ( workingResultSet != null )
		{
			return workingResultSet.iterator( );
		}
		return null;
	}
	/**
	 * Internally walks through the resultset and computes the group breaks
	 * cached for subsequent use
	 * 
	 * @param bGrouped
	 *            Indicates if the resultset contains the group key
	 * 
	 * @return Row indexes containing changing group key values
	 */
	private int[] findGroupBreaks( List resultSet, GroupKey groupKey )
	{
		if ( groupKey == null || groupKey.getKey( ) == null )
		{
			return NO_GROUP_BREAKS;
		}
		
		Collections.sort( resultSet, new TupleComparator( new GroupKey[]{
			groupKey
		} ) );
		final int iColumnIndex = groupKey.getKeyIndex( );