500 error when API auth_token authentication is not sent correctly

[jathanism]

For example, a POST to /api/authenticate/ with an empty payload results in:

Stacktrace (most recent call last):

  File "django/core/handlers/base.py", line 132, in get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "django/views/decorators/csrf.py", line 58, in wrapped_view
    return view_func(*args, **kwargs)
  File "django/views/generic/base.py", line 71, in view
    return self.dispatch(request, *args, **kwargs)
  File "rest_framework/views.py", line 454, in dispatch
    self.response = self.finalize_response(request, response, *args, **kwargs)
  File "rest_framework/views.py", line 374, in finalize_response
    % type(response)
AssertionError: Expected a `Response`, `HttpResponse` or `HttpStreamingResponse` to be returned from the view, but received a `<type 'NoneType'>`

Looks like this related to nsot.api.views.AuthTokenLoginView