title: D3: how to show lone point in a line chart
body: <p>I have some data where few data points may not be available (<code>=== null</code>). To show that data is missing, I am using the <code>line.defined</code> function of d3 (as show <a href="http://bl.ocks.org/mbostock/3035090" rel="nofollow">here</a>) . The problem is that sometimes I have a point which does not have a value on either side and hence does not get displayed on the graph.</p>
  
  <p>Demo: <a href="http://jsfiddle.net/nxrdybdx/3/" rel="nofollow">http://jsfiddle.net/nxrdybdx/3/</a></p>
  
  <p>As you can see, data is missing for April 27 and 29 and so the line is disjoint. Great. The data value on April 28 is non-null but does not get displayed.</p>
  
  <p>I want that a dot gets displayed for April 28. What am I missing? Do I need to add a dot (svg circle) corresponding to each point so that when alone, each point gets displayed on its own?</p>