title: Strange diagonal line in Google Visualization API
body: <p>Sometimes I get a strange diagonal line in my Google Line Chart. Please see below the blue Volume chart. </p>
  
  <p>It is has that "closing" line from the first to the last value.</p>
  
  <p>Any idea how this comes?</p>
  
  <p><a href="https://i.stack.imgur.com/ku48m.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/ku48m.png" alt="strange diagonal line"></a></p>
  
  <pre><code>data = new google.visualization.DataTable()
  data.addColumn('datetime', 'Date')
  data.addColumn('number', 'Volume')
  data.addColumn('number', 'Connected')
  for tracking in trackings
      if(tracking.createdAt instanceof Date &amp;&amp; tracking.volume? &amp;&amp; typeof tracking.volume is "number")
          connected = if(tracking.connected? &amp;&amp; tracking.connected) then 10000 else -10000
          data.addRow([tracking.createdAt, tracking.volume, connected])
  options = {
      title: 'Sensor Values'
      legend:
          position: 'bottom'
      hAxis:
          minValue: from
          maxValue: to
      curveType: 'function'
  }
  chart = new google.visualization.LineChart(document.getElementById('volumeChart'))
  chart.draw(data, options)
  </code></pre>