title: django rest framework " TypeError: 'type' object is not iterable " error
body: <p>I do not know what configuration to modify.</p>
  
  <p>My git repository URL is: <a href="https://github.com/Nomadcoders-Study/Nomadgram" rel="noreferrer">https://github.com/Nomadcoders-Study/Nomadgram</a></p>
  
  <pre><code>Internal Server Error: /images/all/
  Traceback (most recent call last):
    File "/usr/local/var/pyenv/versions/3.6.1/envs/nomadgram/lib/python3.6/site-packages/django/core/handlers/exception.py", line 41, in inner
  response = get_response(request)
    File "/usr/local/var/pyenv/versions/3.6.1/envs/nomadgram/lib/python3.6/site-packages/django/core/handlers/base.py", line 187, in _get_response
  response = self.process_exception_by_middleware(e, request)
    File "/usr/local/var/pyenv/versions/3.6.1/envs/nomadgram/lib/python3.6/site-packages/django/core/handlers/base.py", line 185, in _get_response
  response = wrapped_callback(request, *callback_args, **callback_kwargs)
    File "/usr/local/var/pyenv/versions/3.6.1/envs/nomadgram/lib/python3.6/site-packages/django/views/decorators/csrf.py", line 58, in wrapped_view
  return view_func(*args, **kwargs)
    File "/usr/local/var/pyenv/versions/3.6.1/envs/nomadgram/lib/python3.6/site-packages/django/views/generic/base.py", line 68, in view
  return self.dispatch(request, *args, **kwargs)
    File "/usr/local/var/pyenv/versions/3.6.1/envs/nomadgram/lib/python3.6/site-packages/rest_framework/views.py", line 478, in dispatch
  request = self.initialize_request(request, *args, **kwargs)
    File "/usr/local/var/pyenv/versions/3.6.1/envs/nomadgram/lib/python3.6/site-packages/rest_framework/views.py", line 380, in initialize_request
  authenticators=self.get_authenticators(),
    File "/usr/local/var/pyenv/versions/3.6.1/envs/nomadgram/lib/python3.6/site-packages/rest_framework/views.py", line 274, in get_authenticators
    return [auth() for auth in self.authentication_classes]
  TypeError: 'type' object is not iterable
  </code></pre>