Ensure split-test group zero content is protected

TNL-4771

lms/djangoapps/course_blocks/transformers/split_test.py

@@ -66,7 +66,7 @@ class SplitTestTransformer(BlockStructureTransformer):
             for child_location in xblock.children:
                 child = block_structure.get_xblock(child_location)
                 group = child_to_group.get(child_location, None)
-                child.group_access[partition_for_this_block.id] = [group] if group else []
+                child.group_access[partition_for_this_block.id] = [group] if group is not None else []
 
     def transform(self, usage_info, block_structure):
         """