title: MongoKitten: check if ObjectId exist
body: <p>How to check if ObjectId exist in collection?
  From mongo console I do it:</p>
  
  <pre><code>&gt; db.collection.find({_id: ObjectId("5bb216a8475fe42644993a40")}, {_id: 1}).limit(1);
  </code></pre>
  
  <p>How to do the same using MongoKitten?</p>