title: What parameters are passed to Mongoose callbacks
body: <p>In the <a href="http://mongoosejs.com/docs/api.html#model_Model.findOneAndUpdate" rel="noreferrer">mongoose documentation</a> it frequently lists an optional callback for certain query operators (like <code>findOneAndUpdate</code>), however, it does not mention what parameters (arguments) the callback takes. What are they, and how would I find out?</p>
  
  <p>Also, if <code>conditions</code>, <code>update</code> etc. are optional, and I want to specify a callback at the end, do I have to pass in the <code>null</code> value, or empty objects or can I just specify the callback -- and hose does Mongoose know?</p>
  
  <p><code>Model.findOneAndUpdate([conditions], [update], [options], [callback])</code></p>