Representing "No value" in array in Google visualization

For the below array i get a smooth curve.

  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]);
  开发者_开发百科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]);

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?

If I make it like data.addRow(["D", 8, , 1]); the graph becomes discontinuous at the D for Blankets.

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.

What you are looking for is the option:

interpolateNulls = true;

And then you just put a 'null' into the value array at the point where data is missing.

Check the API reference: http://code.google.com/apis/chart/interactive/docs/gallery/linechart.html#Configuration_Options