title: dimple.js Show X Axis label, but if "value" is null don't place a circle on chart
body: <p>Question: How do I show the Date Value on the X Axis, but not show the circle in the chart area if it is null?</p>
  
  <p>So I am playing around with Dimple.js and I have created a PHP function that pulls data from my MySql database, and maps out when certain trucks arrived to a location by hours.  So the X Axis is the date and the Y Axis is the military time it arrived.  I use the Min date and max date as the begin and end to loop through.  I want to show each day between min and max on the x axis, so if no trucks arrived I assign Value = Null for that. </p>
  
  <p>The problem is there are now circles on the bottom of my chart along the 0 section of the y axis for these nulls.  I don't know how to check if value is zero don't show the circle, but still show the date on the X Axis.  The data is structured as below:</p>
  
  <pre><code>$dataset_progress005[] = array('Date' =&gt; $truck_arrive_day,
        'Value' =&gt; $truck_arrive_time,
        'Move ID' =&gt; $move_inbound_time_id);
  </code></pre>
  
  <p>with the javascript as this....</p>
  
  <pre><code>&lt;script type="text/javascript"&gt; &lt;!--Example Plot Chart....--&gt;
          var svg = dimple.newSvg("#area_progress_report5", 800, 400);
  
          var data = &lt;?php echo json_encode($dataset_progress005); ?&gt;;
  
          var myChart = new dimple.chart(svg, data);
          myChart.setBounds(60, 30, 505, 305)
          var x = myChart.addCategoryAxis("x", "Date");
          //var x = myChart.addTimeAxis("x", "Date");
          //var x = myChart.addMeasureAxis("x", "Date");
          x.addOrderRule("Date");
          myChart.addCategoryAxis("y", "Value");
          myChart.addSeries("Move ID", dimple.plot.bubble);
          myChart.draw();
  
          x.shapes.selectAll("text").attr("transform",
              function (d) {
                return d3.select(this).attr("transform") + " translate(0, 40) rotate(-90)";
              });
  
       &lt;/script&gt;
  </code></pre>
  
  <p>Question: How do I show the Date Value on the X Axis, but not show the circle in the chart area if it is null?</p>