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
* 
	 * @param a
	 *            Object one
	 * @param b
	 *            Object two
	 * 
	 * @return The result of the comparison
	 */
	public static int compareObjects( Object a, Object b )
	{
		
		if ( a == null && b == null )
		{
			return 0;
		}
		
		else if ( a == null && b != null )
		{
			return -1;
		}
		
		else if ( a != null && b == null )
		{
			return 1;
		}
		else if ( a instanceof String )
		{
			int iC = a.toString( ).compareTo( b.toString( ) );
			if ( iC != 0 )
				iC = ( ( iC < 0 ) ? -1 : 1 );