title: PivotTable.js - sum aggregator does not show zeros
body: <p>I am using PivotTable.js to pivot some data for a report. In the report, I have a need to show rows for which the aggregate sum is zero, and would like to display that zero in the totals column. When using the aggregatorTemplates.sum, the aggregate sum of zeros seems to be a black cell. I wonder if there is a way to render the zero?</p>
  
  <p>A simplified example of what I'm doing is</p>
  
  <pre><code>var sum = $.pivotUtilities.aggregatorTemplates.sum;
  var numberFormat = $.pivotUtilities.numberFormat;
  var intFormat = numberFormat({digitsAfterDecimal: 0});
  
  $("#output").pivot(
    [
      {color: "green", shape: "null", value: 0},
      {color: "blue", shape: "circle", value: 1},
      {color: "red", shape: "triangle", value: 2},
      {color: "blue", shape: "circle", value: 3},
      {color: "red", shape: "triangle", value: 4}
    ],
    {
      rows: ["color"],
      cols: ["shape"],
      aggregator: sum(intFormat)(["value"])
    }
  );
  </code></pre>
  
  <p>This is the example from <a href="https://pivottable.js.org/examples/simple_agg.html" rel="nofollow noreferrer">https://pivottable.js.org/examples/simple_agg.html</a>, modified to illustrate the issue I'm facing. This is also available in a fiddle <a href="https://jsfiddle.net/rgs258/dky0hh1y/" rel="nofollow noreferrer">https://jsfiddle.net/rgs258/dky0hh1y/</a>.</p>
  
  <p>As a secondary question, I wonder if there's a way to hide the 'null' column in my example?</p>
  
  <p>Any help or advice in resolving this is appreciated.</p>