title: Representing "No value" in array in Google visualization
body: <p>For the below array i get a smooth curve.     </p>
  
  <pre><code>  data.addColumn('string', 'x');
    data.addColumn('number', 'Cats');
    data.addColumn('number', 'Blanket 1');
    data.addColumn('number', 'Blanket 2');
    data.addRow(["A", 1, 1, 0.5]);
    data.addRow(["B", 2, 0.5, 1]);
    data.addRow(["C", 4, 1, 0.5]);
    data.addRow(["D", 8, 7 , 1]);
    data.addRow(["E", 7, 1, 0.5]);
    data.addRow(["F", 7, 0.5, 1]);
    data.addRow(["G", 8, 1, 0.5]);
    data.addRow(["H", 4, 0.5, 1]);
    data.addRow(["I", 2, 1, 0.5]);
    data.addRow(["J", 3.5, 0.5, 1]);
    data.addRow(["K", 3, 1, 0.5]);
    data.addRow(["L", 3.5, 0.5, 1]);
    data.addRow(["M", 1, 1, 0.5]);
    data.addRow(["N", 1, 0.5, 1]);
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/ifsHw.jpg" alt="enter image description here"></p>
  
  <p>Now assume that I don't have the Blanket1 value for row D, how do I represent it so that there is coninuity in the graph?</p>
  
  <p>If I make it like <code>data.addRow(["D", 8, , 1]);</code> the graph becomes discontinuous at the D for Blankets.</p>
  
  <p><img src="https://i.stack.imgur.com/7ItkO.jpg" alt="enter image description here"></p>
  
  <p>I want google to make a guess at that value and keep the curve smooth. Even if the guess is not smart that is fine but the curve should be continuous and smooth.</p>