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
final int[] iaColumnIndexes = new int[n];
		String sExpressionKey;
		for ( int i = 0; i < n; i++ )
		{
			sExpressionKey = ( (Query) elExpressionKeys.get( i ) ).getDefinition( );
			iaColumnIndexes[i] = ( (Integer) htLookup.get( sExpressionKey ) ).intValue( );
		}
		return new ResultSetDataSet( this,
				iaColumnIndexes,
				( iGroupIndex <= 0 ) ? 0 : iaGroupBreaks[iGroupIndex - 1],
				( iGroupIndex > iaGroupBreaks.length - 1 ) ? 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 iGroupIndex
	 *            The group number for which a subset is requested
	 * @param sExpressionKeys
	 *            The expression columns for which a subset is requested
	 * 
	 * @return An instance of the resultset subset
	 */
	public ResultSetDataSet getSubset( int iGroupIndex, String[] sExpressionKeys )
	{
		if ( sExpressionKeys == null )
		{
			return null;