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 new ResultSetDataSet( this,
				new int[]{
					iColumnIndex
				},
				( iGroupIndex <= 0 ) ? 0 : iaGroupBreaks[iGroupIndex - 1],
				( iGroupIndex >= iaGroupBreaks.length ) ? getRowCount( )
						: iaGroupBreaks[iGroupIndex] );
	}
	/**
	 * Creates an instance of a resultset subset that uses references to
	 * dynamically compute a subset of the original resultset instance rather
	 * than duplicate a copy of the original resultset data content
	 * 
	 * @param elExpressions
	 *            The expression columns for which a resultset subset is being
	 *            requested
	 * 
	 * @return The resultset subset containing the requested columns and all
	 *         rows of the resultset
	 */
	public ResultSetDataSet getSubset( EList elExpressions )
			throws ChartException
	{
		final int n = elExpressions.size( );
		final int[] iaColumnIndexes = new int[n];
		String sExpression;
		try
		{
			for ( int i = 0; i < n; i++ )
			{