Javascript：如何只绘制某些值

Question

对于下面的代码，我如何摆脱May的值，但保持图形从4月到6月没有5月下降到零？：

jsfiddle：http://jsfiddle.net/leighking2/sLgefm04/6/

 var data = {
    labels: ["January", "February", "March", "April", "May", "June", "July"],
    datasets: [{
            label: "My First dataset",
            fillColor: "rgba(220,220,220,0.2)",
            strokeColor: "rgba(220,220,220,1)",
            pointColor: "rgba(220,220,220,1)",
            pointStrokeColor: "#fff",
            pointHighlightFill: "#fff",
            pointHighlightStroke: "rgba(220,220,220,1)",
            data: [65, null, null, 81, 56, 55, 40]
        },