CFF Stacked Bar

Hi, I am trying to build a stacked bar chart with chart.js but it seems that CFF does not accept my “stacked” option, it just places bars side by side. This is my sample code. What have I done wrong?

CFFCHART(
        'my-chart',
        {
            type:'bar',
            data:{
                labels:['Label A', 'Label B', 'Label C'],
                    datasets:[
                        {
                            label:'Previsions',
                            data:[300, 400, 500]
                        },
                        {
                            label:'Real',
                            data:[fieldname1, fieldname2, fieldname5]
                        }
                    		]
                    		},
        	options: {
    			responsive: true,
    			scales: {
      x: {
        stacked: true,
      },
      y: {
        stacked: true
      }
    }
					}
        		}
    );