title: InvalidBasesError: Cannot resolve bases for [<ModelState: 'users.GroupProxy'>]
body: <p>When I run tests I get this error during database initialization:</p>
  
  <pre><code>django.db.migrations.state.InvalidBasesError: Cannot resolve bases for [&lt;ModelState: 'users.GroupProxy'&gt;]
  This can happen if you are inheriting models from an app with migrations (e.g. contrib.auth)
  </code></pre>
  
  <p>I created this proxy for contrib.auth Group model to place it in my app in django admin:</p>
  
  <pre><code>class GroupProxy(Group):
      class Meta:
          proxy = True
          verbose_name = Group._meta.verbose_name
          verbose_name_plural = Group._meta.verbose_name_plural
  </code></pre>
  
  <p>So what can I do to fix this issue?</p>