Pb with Stacked Bar

I’m trying to display a graph, horizontal bars (Stacked Horizontal Bar) with dhtmlXChart.
But when the value of an item is 0, it must display nothing.
I think we should use this code in the definition of the label.

barChart1.define('label',function(obj){ if (obj.thisItemValue == 0){ return ''; }else{ return obj.thisItemValue ; } });
But I can not find the name of the property (thisItemValue ???)which gives me the value of the item that is being displayed.Can you help me?