title: Using Highcharts formatter causes Cannot read property 'length' of undefined
body: <p>I want to display custom text in tooltip. When I use my code, I got <code>Cannot read property 'length' of undefined</code> when I hover on tooltip. </p>
  
  <p>Does someone knows where's the problem?</p>
  
  <pre><code>tooltip: {
              shared: false,
              formatter: function() {
                  var serie = this.series;
                  var s = '&lt;span style="color:' + serie.color + '"&gt;' + serie.options.name + '&lt;/span&gt;: &lt;b&gt;' + this.y + '&lt;/b&gt;&lt;br/&gt;';
                  $.each(serie.options.composition, function(name, value) {//Error pop ups here
                      s += '&lt;b&gt;' + name + ':&lt;/b&gt; ' + value + '&lt;br&gt;';
                  });
                  return s;
              }
          }
  </code></pre>
  
  <p>EDIT - Added error message:</p>
  
  <pre><code>    Uncaught TypeError: Cannot read property 'length' of undefinedm.extend.each @ jquery.min.js:2$.highcharts.tooltip.formatter @ grafovi.php:823Mb.refresh @ highcharts.js:160Va.runPointActions @ highcharts.js:166Va.onContainerMouseMove @ highcharts.js:174Va.setDOMEvents.b.onmousemove @ highcharts.js:176
  </code></pre>