title: EXTJS 5 Not display empty record in chart
body: <p>First: Here is the fiddle that explains clearly my problem  : <a href="https://fiddle.sencha.com/#fiddle/hgm" rel="nofollow noreferrer">https://fiddle.sencha.com/#fiddle/hgm</a></p>
  
  <p>To sum up, I have a very simple chart bound to a store. The store has few "empty" records and is like this:</p>
  
  <pre><code>var storeA = Ext.create('Ext.data.Store', {
      fields: ['name', 'value', 'length'],
      data: [
          {"name": "A-0", "value": 18.34, "length": 30},
          {"name": "A-1", "value": 2.67, "length": 35},
          {"name": "", "value": 0, "length": 0} // this is what I call an empty record
      ]
  });
  </code></pre>
  
  <p>My pie chart is very simple:</p>
  
  <pre><code>var donut = Ext.create('Ext.chart.PolarChart', {
      title: 'Test',
      animation: true,
      width: 300,
      height: 300,
      renderTo: Ext.getBody(),
  
      store: storeA,
  
      legend: {
          docked: 'bottom'
      },
  
      series: [{
          type: 'pie',
          angleField: 'value',
          lengthField: 'length',
          colors: ["#9aff4f", "#35b4e3", "#ffb400"],
          donut: 20,
          label: {
              field: 'name',
              display: 'inside'
          },
          highlight: true
      }]
  });
  </code></pre>
  
  <p>But I would like that the empty record does not appear in the legend like it does actually:</p>
  
  <p><img src="https://i.stack.imgur.com/VbPCa.png" alt="enter image description here"></p>
  
  <p>I would like to add that I don't want to clean the store before giving it to the chart. I need to use this exact same store.</p>