Using display_name_with_default instead of display_name.

TNL-4103

openedx/core/djangoapps/bookmarks/tasks.py

@@ -32,7 +32,7 @@ def _calculate_course_xblocks_data(course_key):
             usage_id = unicode(current_block.scope_ids.usage_id)
             block_info = {
                 'usage_key': current_block.scope_ids.usage_id,
-                'display_name': current_block.display_name,
+                'display_name': current_block.display_name_with_default,
                 'children_ids': [unicode(child.scope_ids.usage_id) for child in children]
             }
             blocks_info_dict[usage_id] = block_info

openedx/core/djangoapps/bookmarks/tests/test_tasks.py

@@ -4,7 +4,7 @@
 import ddt
 
 from xmodule.modulestore import ModuleStoreEnum
-from xmodule.modulestore.tests.factories import check_mongo_calls
+from xmodule.modulestore.tests.factories import check_mongo_calls, ItemFactory
 
 from ..models import XBlockCache
 from ..tasks import _calculate_course_xblocks_data, _update_xblocks_cache
@@ -164,3 +164,19 @@ def test_update_xblocks_cache(self, course_attr, expected_sql_queries):
 
         with self.assertNumQueries(3):
             _update_xblocks_cache(course.id)
+
+    def test_update_xblocks_cache_with_display_name_none(self):
+        """
+        Test that the xblocks data is persisted correctly with display_name=None.
+        """
+        ItemFactory.create(parent_location=self.sequential_2.location, category='vertical', display_name=None)
+
+        _update_xblocks_cache(self.course.id)
+
+        for usage_key, __ in self.course_expected_cache_data.items():
+            xblock_cache = XBlockCache.objects.get(usage_key=usage_key)
+            for path_index, path in enumerate(xblock_cache.paths):
+                for path_item_index, path_item in enumerate(path):
+                    self.assertEqual(
+                        path_item.usage_key, self.course_expected_cache_data[usage_key][path_index][path_item_index + 1]
+                    )