Show 404 page when the topic is not found.

Earlier it was failing with internal error.

community/www/courses/topic.py

@@ -2,12 +2,16 @@ import frappe
 
 def get_context(context):
     context.no_cache = 1
-    course_name = get_queryparam("course", '/courses')
-    context.course = get_course(course_name)
 
-    topic_name = get_queryparam("topic", '/courses?course=' + course_name)
-    context.topic = get_topic(course_name, topic_name)
-    context.livecode_url = get_livecode_url()
+    try:
+        course_name = get_queryparam("course", '/courses')
+        context.course = get_course(course_name)
+
+        topic_name = get_queryparam("topic", '/courses/' + course_name)
+        context.topic = get_topic(course_name, topic_name)
+        context.livecode_url = get_livecode_url()
+    except frappe.DoesNotExistError:
+        context.template = 'www/404.html'
 
 def get_livecode_url():
     doc = frappe.get_doc("LMS Settings")
@@ -23,15 +27,15 @@ def get_queryparam(name, redirect_when_not_found):
 def get_course(name):
     try:
         course = frappe.get_doc('LMS Course', name)
-    except frappe.exceptions.DoesNotExistError:
-        raise frappe.NotFound
+    except frappe.DoesNotExistError:
+        raise
     return course
 
 def get_topic(course_name, topic_name):
     try:
         topic = frappe.get_doc('LMS Topic', topic_name)
-    except frappe.exceptions.DoesNotExistError:
-        raise frappe.NotFound
+    except frappe.DoesNotExistError:
+        raise
     if topic.course != course_name:
-        raise frappe.NotFound
+        raise frappe.DoesNotExistError()
     return topic