title: Update by Id not finding document
body: <p>I am attempting to perform a relatively simple update using Mongoose:</p>
  
  <pre><code>var location =  locationService.getLocation(typedLat, typedLong, travelRadius);
  
  DocumentModel.update({_id :  passedInId }, { location : location }, function(err, resp){
      next(err, resp);
  });
  </code></pre>
  
  <p>In this case passedInId is the string:
  "561ee6bbe4b0f25b4aead5c8"</p>
  
  <p>And in the object (test data I created) the id is:
  "_id": ObjectId("561ee6bbe4b0f25b4aead5c8")</p>
  
  <p>When I run the above however, matched documents is 0. I assume this is because passedInId is being treated like a string, however when I type it to an ObjectId:</p>
  
  <pre><code>var queryId = ObjectId(passedInId)
  </code></pre>
  
  <p>The result is the same, the document doesn't match.  What am I missing? This seems like it should be obvious....</p>