title: Underscore sortBy
body: <pre><code> var array =  [{"id":"0", "stopDate":null},
                 {"id":"1", "stopDate":"10/06/2014"},
                 {"id":"2", "stopDate":null},
                 {"id":"3", "stopDate":"09/06/2014"}];
  </code></pre>
  
  <p>I have array of objects as above and want to sort by stop date using underscore. I am using following function to do so.</p>
  
  <pre><code>_.sortBy(array, "stopDate"); // asc
  _.sortBy(array, "stopDate").reverse(); //desc
  </code></pre>
  
  <p>Above method sorts the date value properly but ignores null. So the output for asc is coming out to be</p>
  
  <pre><code>var actual=  [{"id":"0", "stopDate":null},
                {"id":"3", "stopDate":"09/06/2014"},
                {"id":"2", "stopDate":null},
                {"id":"1", "stopDate":"10/06/2014"}];
  </code></pre>
  
  <p>But I am expecting null to be grouped together and should appear one after other.</p>
  
  <pre><code>var expected=  [{"id":"0", "stopDate":null},
                  {"id":"2", "stopDate":null},
                  {"id":"3","stopDate":"09/06/2014" },
                  {"id":"1", "stopDate":"10/06/2014"}];
  </code></pre>