How to get the total amount refunded in Stripe using Keen IO

gistfile1.js

Keen.onChartsReady(function() {
  var metric = new Keen.Metric("Stripe_Events", {
    analysisType: "sum",
    targetProperty: "data.object.amount_refunded",
    filters: [{"property_name":"type","operator":"eq","property_value":"charge.refunded"}]
  });
  metric.draw(document.getElementById("someDiv"));
});