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
* Indicates whether base series grouping was applied on the resultset to
	 * prevent duplicate grouping.
	 */
	private boolean bBaseGroupingApplied = false;
	private final GroupKey[] oaGroupKeys;
	/**
	 * A reusable instance that indicates no group breaks
	 */
	private static final int[] NO_GROUP_BREAKS = new int[0];
	private static ILogger logger = Logger.getLogger( "org.eclipse.birt.chart.engine/datafeed" ); 
	/**
	 * The default constructor that allows creation of a resultset wrapper
	 * 
	 * @param stExpressionKeys
	 *            The set of expressions associated with each column in the
	 *            resultset
	 * @param liResultSet
	 *            A list of rows that represent the actual resultset data
	 *            content. Each row contains an Object[]
	 * @param groupKeys
	 *            An array of orthogonal grouping keys, if it's null or
	 *            zero-length, no orthogonal grouping used.
	 */
	public ResultSetWrapper( Collection stExpressionKeys, List liResultSet,
			GroupKey[] groupKeys )
	{
		rawResultSet = liResultSet;
		workingResultSet = new ArrayList( );
		workingResultSet.addAll( rawResultSet );
		saExpressionKeys = (String[]) stExpressionKeys.toArray( new String[stExpressionKeys.size( )] );