title: Django loaddata returns DeserializationError: 'NoneType' object has no attribute '_meta'
body: <p>I have a json file coming from a dumpdata that I want to load and when doing loaddata after some time it returns this message:</p>
  
  <p><code>DeserializationError: 'NoneType' object has no attribute '_meta'</code></p>
  
  <p>There is no clue, no reference, I have no idea where this is coming from. I have tried with Django 1.4.8 and 1.5.4 and the result is the same.</p>
  
  <p>What could it be?</p>
  
  <p>edit: I have added a pdb to find out more and it appears that the objects that trigger the error are from auth.permission.</p>