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
}
	/**
	 * 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 sExpressionKeys
	 *            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( String[] sExpressionKeys )
			throws ChartException
	{
		if ( sExpressionKeys == null )
		{
			return null;
		}
		final int n = sExpressionKeys.length;
		final int[] iaColumnIndexes = new int[n];
		String sExpression;
		try
		{
			for ( int i = 0; i < n; i++ )
			{
				sExpression = sExpressionKeys[i];
				iaColumnIndexes[i] = ( (Integer) htLookup.get( sExpression ) ).intValue( );
			}