title: Creating clean Vapor project (using fluent) results in MongoKitten runtime error
body: <p>I managed to setup Vapor with MongoDB and get it working but if I do a new clean project I get runtime error from MongoKitten. In detail:</p>
  
  <p>I have an outdated vapor project that works fine from 27/07/2017.
  I do the same exactly project now 24/10/2017.
  When it compiles for the first time I get the following warning (don't know if is relevant to the following error):</p>
  
  <p><a href="https://i.stack.imgur.com/j3bNj.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/j3bNj.png" alt="Warning Screenshot"></a></p>
  
  <p>Compilation finishes and I get the following error when I run the project:</p>
  
  <p><a href="https://i.stack.imgur.com/MfpoQ.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/MfpoQ.png" alt="Error Screenshot"></a></p>
  
  <p>I only know that this is caused by the preparation step in main.swift e.g. here:</p>
  
  <pre><code>config.preparations.append(User.self)
  </code></pre>
  
  <p>Without this step I dont get any runtime error (but fluent connection to mongodb isn't working properly either).</p>
  
  <p>My config is pretty simple:</p>
  
  <p><a href="https://i.stack.imgur.com/TlvY9.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/TlvY9.png" alt="Config Screenshot"></a></p>
  
  <p>This happens in Swift 3.1.1 but same happens in Swift 4.0. Environment is Ubuntu 17.04.</p>
  
  <p>How can I solve this?</p>