title: Pass null values to SVG path (using d3.js) to suppress missing data
body: <p>Using jQuery Flot, I can pass a <code>null</code> value to the plotting mechanism so it just won't draw anything on the plot. See how the missing records are suppressed:</p>
  
  <p><img src="https://i.stack.imgur.com/zpPka.png" alt="enter image description here"></p>
  
  <p>I'm looking to move to <code>d3js</code>, so that I can have deeper low level control of the graphics using SVG. However, I have yet to find out how to do that same process of suppressing missing records. The image below is an attempt to do this, using a value of <code>0</code> instead of <code>null</code> (where the <code>d3</code> package breaks down). Here is some code to give you an idea of how I produced the graph below:</p>
  
  <pre class="lang-js prettyprint-override"><code>var line = d3.svg.line()
      .x(function(d) {
         var date = new Date(d[0]);
         return x(date);
      })
      .y(function(d) {
         var height = d[1]; 
         if (no_record_exists) {
             return y(0);
         }
         return y(height) + 0.5;
      });
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/Gh9ae.png" alt="enter image description here"></p>
  
  <p>I looked up the SVG <code>path</code> element at the Mozilla Developer Network, and I found out that there is a MoveTo command, <code>M x y</code>, that only moves the "pen" to some point without drawing anything. Has this been implemented in the <code>d3js</code> package, so that I won't have to create several <code>path</code> elements every time I encounter a missing record?</p>