Deal with NoneType access.

The `NoneType` object is not available from the `types` module in
python 3. This is a workaronud to deal with that.

lms/djangoapps/discussion/django_comment_client/permissions.py

@@ -6,7 +6,6 @@ Module for checking permissions with the comment_client backend
 from __future__ import absolute_import
 
 import logging
-from types import NoneType
 
 import six
 from edx_django_utils.cache import DEFAULT_REQUEST_CACHE
@@ -23,7 +22,7 @@ from openedx.core.lib.cache_utils import request_cached
 
 
 def has_permission(user, permission, course_id=None):
-    assert isinstance(course_id, (NoneType, CourseKey))
+    assert isinstance(course_id, (type(None), CourseKey))
     request_cache_dict = DEFAULT_REQUEST_CACHE.data
     cache_key = "django_comment_client.permissions.has_permission.all_permissions.{}.{}".format(
         user.id, course_id