title: Using Morris.js line chart, do not show point for empty value
body: <p>I'm using Morris.js to create a line graph.<br>
  Data is returned to me like this:</p>
  
  <pre><code>[{XValue:1,YValue1:1007,Yvalue2:1014},
  {XValue:2,YValue1:1023,Yvalue2:1029},
  {XValue:3,YValue1:0,Yvalue2:1041},
  {XValue:4,YValue1:0,Yvalue2:1056},...];
  </code></pre>
  
  <p>I don't want to display 0 values, so I am replacing the zeroes with '' in my json prior to giving it morris to render:  </p>
  
  <pre><code> for (var i = 0; i &lt; json.length; i++) {
       if (json[i].YValue1 == 0) {
           json[i].YValue1 = '';
       }
   }
  
  Morris.Line({
      element: 'TotalLoad',
      data: json,
      xkey: 'XValue',
      ykeys: ['YValue1','YValue2'],
      ymin: 1000,
      ymax: 3000,
      parseTime: false,
      labels: ['Actual', 'Forecast'],
      events: [hour - 1],
      eventStrokeWidth: 2,
      continuousLine: false
  });
  </code></pre>
  
  <p>My output looks like this:<a href="http://i.stack.imgur.com/BW2ZR.png" rel="nofollow">Morris Chart</a></p>
  
  <p>The Y Values with no value show no line(which is the intended effect) but the point still appears at the top of the graph, although it is half cut off.  The label shows 'NaN', which is fine with me if I can get the point to disappear!</p>