title: Django using "." as primary key gives 404
body: <p>I am using DRF along with drf-nested-routers to configure my routing. I have an api route structure this way.</p>
  
  <p><code>/posts/1/comments</code></p>
  
  <p>Now instead of using the id I have decided to use the name of the object instead.</p>
  
  <p><code>/posts/mypost/comments</code></p>
  
  <p>This works perfectly but an issue occurs when a <code>.</code> is being added to the key.</p>
  
  <p><code>/posts/my.post/comments</code></p>
  
  <p>When including a <code>.</code> as part of the key for the resource, it returns a <code>404</code> error on Django. I have been trying to debug this issue to no avail.</p>