title: Google Charts Tooltips only works with a first row that has no tooltips
body: <p>I'm trying to use tooltips in a google bar chart, and am running into a weird issue where my tooltips only work if the top row of my datatable has no tooltips in it. </p>
  
  <p>When I do this, the chart doesn't render:</p>
  
  <pre><code>function drawVisualization() {
    // Create and populate the data table.
      var data = google.visualization.arrayToDataTable([
      ['Report','Ineffective', 'Developing', 'Effective', 'Highly Effective'],
      ['Growth Rating',{v:18, f:'tooltip text'},{v:12, f:'tooltip text'},{v:66, f:'tooltip text'},{v:4, f:'tooltip text'}],
      ['Composite Rating',{v:6, f:'tooltip text'},{v:12, f:'tooltip text'},{v:58, f:'tooltip text'},{v:25, f:'tooltip text'}]
    ]);
  
    // Create and draw the visualization.
       new google.visualization.BarChart(document.getElementById('chart_div')).
        draw(data,
         {title:"TITLE",
          colors: ['#638FBC','#FFE17C','#FFA87C','#204C7A'],
          hAxis: {title: "Percent of Educators", viewWindow:{max:105, min:0}, titleTextStyle: {italic: false}},
          chartArea: {width: "60%"},
         isStacked: true}
        );
  }
  </code></pre>
  
  <p>but if I do this, the chart renders fine</p>
  
  <pre><code>function drawVisualization() {
    // Create and populate the data table.
      var data = google.visualization.arrayToDataTable([
      ['Report','Ineffective', 'Developing', 'Effective', 'Highly Effective'],
      ['Empty', 0 ,   0 , 0   , 0   ],
      ['Growth Rating',{v:18, f:'tooltip text'},{v:12, f:'tooltip text'},{v:66, f:'tooltip text'},{v:4, f:'tooltip text'}],
      ['Composite Rating',{v:6, f:'tooltip text'},{v:12, f:'tooltip text'},{v:58, f:'tooltip text'},{v:25, f:'tooltip text'}]
    ]);
  
    // Create and draw the visualization.
       new google.visualization.BarChart(document.getElementById('chart_div')).
        draw(data,
         {title:"TITLE",
          colors: ['#638FBC','#FFE17C','#FFA87C','#204C7A'],
          hAxis: {title: "Percent of Educators", viewWindow:{max:105, min:0}, titleTextStyle: {italic: false}},
          chartArea: {width: "60%"},
         isStacked: true}
        );
  </code></pre>
  
  <p>I have no idea why adding that extra row makes it work.</p>
  
  <p>Any help would be greatly appreciated.</p>