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 The number of rows of data associated with the resultset wrapper
	 *         instance
	 */
	public int getRowCount( )
	{
		return workingResultSet.size( );
	}
	/**
	 * Extracts the group's key value that remains unchanged for a given group
	 * 
	 * @param iGroupIndex
	 *            The group index for which the key is requested
	 * @param sExpressionKey
	 *            The expression column that holds the group key value
	 * 
	 * @return The group key value associated with the requested group index
	 */
	public Object getGroupKey( int iGroupIndex, String sExpressionKey )
	{
		if ( !htLookup.containsKey( sExpressionKey ) )
		{
			return IConstants.UNDEFINED_STRING;
		}
		final int iColumnIndex = ( (Integer) htLookup.get( sExpressionKey ) ).intValue( );
		final int iRow = ( iGroupIndex <= 0 ) ? 0
				: iaGroupBreaks[iGroupIndex - 1];
		if ( iRow >= 0 && iRow < workingResultSet.size( ) )
		{
			return ( (Object[]) workingResultSet.get( iRow ) )[iColumnIndex];
		}