fix(ban): Add defensive coding for get_banned_usernames and get_user_ban_scope

Author: mraman-2U

lms/djangoapps/discussion/rest_api/api.py

@@ -1957,10 +1957,13 @@ def get_course_discussion_user_stats(
 
     # Exclude banned users from the learners list
     # Get all active bans for this course using forum API
-    banned_usernames = forum_api.get_banned_usernames(
-        course_id=course_key,
-        org_key=course_key.org
-    )
+    get_banned_usernames = getattr(forum_api, 'get_banned_usernames', None)
+    banned_usernames = []
+    if get_banned_usernames:
+        banned_usernames = get_banned_usernames(
+            course_id=course_key,
+            org_key=course_key.org
+        )
 
     # Filter out banned users from the stats
     if banned_usernames:

lms/djangoapps/discussion/rest_api/serializers.py

@@ -328,7 +328,10 @@ def get_author_ban_scope(self, obj):
             if isinstance(course_id, str):
                 course_id = CourseKey.from_string(course_id)
 
-            return forum_api.get_user_ban_scope(user, course_id)
+            get_user_ban_scope = getattr(forum_api, 'get_user_ban_scope', None)
+            if get_user_ban_scope:
+                return get_user_ban_scope(user, course_id)
+            return None
         except (ObjectDoesNotExist, ValueError, Exception):  # pylint: disable=broad-exception-caught
             return None