Remove Percentage Completed from Tooltip in google gantt chart

I am using google chart to show the Gantt chart. The chart is working fine but when i hover on the chart bar, I am seeing Percentage Completed in the tooltip.

Below is the HTML of the same

  <html>
<head>
  <script type="text/javascript" src="https://www.gstatic.com/charts/loader.js"></script>
  <script type="text/javascript">
    google.charts.load('current', {'packages':['gantt']});
    google.charts.setOnLoadCallback(drawChart);

    function drawChart() {

      var data = new google.visualization.DataTable();
      data.addColumn('string', 'Task ID');
      data.addColumn('string', 'Task Name');
      data.addColumn('date', 'Start Date');
      data.addColumn('date', 'End Date');
      data.addColumn('number', 'Duration');
      data.addColumn('number', 'Percent Complete');
      data.addColumn('string', 'Dependencies');

      data.addRows([
        ['Research', 'Find sources',
         new Date(2015, 0, 1), new Date(2015, 0, 5), null,  100,  null],
        ['Write', 'Write paper',
         null, new Date(2015, 0, 9), daysToMilliseconds(3), 25, 'Research,Outline'],
        ['Cite', 'Create bibliography',
         null, new Date(2015, 0, 7), daysToMilliseconds(1), 20, 'Research'],
        ['Complete', 'Hand in paper',
         null, new Date(2015, 0, 10), daysToMilliseconds(1), 0, 'Cite,Write'],
        ['Outline', 'Outline paper',
         null, new Date(2015, 0, 6), daysToMilliseconds(1), 100, 'Research']
      ]);

      var options = {
        height: 400,
        gantt: {
          trackHeight: 30
        }
      };

      var chart = new google.visualization.Gantt(document.getElementById('chart_div'));

      chart.draw(data, options);
    }
  </script>
</head>
<body>
  <div id="chart_div"></div>
</body>
</html>

I can somehow, successfully hide the Resource name column but when I remove the Percentage completed column, I am getting errors like column and row mismatch, the value should not be null, etc.

Can anyone please let me know if there is any way to hide the percent completed value from the tooltip?

Thanks!