diff --git a/recommendation_engine.py b/recommendation_engine.py
index 59a26cd..110e524 100644
--- a/recommendation_engine.py
+++ b/recommendation_engine.py
@@ -119,11 +119,15 @@ class Engine:
             return self.get_recommendations(user)
 
         else:
+            if play_index is None:
+                video_indx = list(range(video_num))
+                random.shuffle(video_indx)
+            else:
             # played index is excluded from the random shuffle and deterministically added to staySame pool.
-            video_indx = [*range(play_index)]+[*range(play_index+1,video_num)]
-            # video_indx = list(range(video_num))
-            random.shuffle(video_indx)
-            video_indx.append(play_index)
+                video_indx = [*range(play_index)]+[*range(play_index+1,video_num)]
+                random.shuffle(video_indx)
+                video_indx.append(play_index)
+
             next_clip_index = video_indx[:nc]
             next_playlist_index = video_indx[nc:nc+np]
             stay_same_index = video_indx[nc+np:]
@@ -131,28 +135,37 @@ class Engine:
             rec_list = []
             # select next clip for nextClip pool except when the playlist has only one clip. 
             for i in next_clip_index:
-                for playlist in self.playlists:
-                    if playlist.get('name')== prev_grid_list[i].get('playlist'):
-                        if len(playlist["clips"]) == 1:
-                            next_playlist_index.append(i)
-                            break
-                        # Discuss how this behavour should be: should it switch to a new playlist if it is the end of the playlist clip sequence already?
-                        elif prev_grid_list[i].get('playlistPosition', 0) + 1 == len(playlist['clips']):
-                            playlist_pos = 0
-                        else:
-                            playlist_pos = prev_grid_list[i].get('playlistPosition', 0) + 1
-                        
-                        rec_list.append((i, {
-                            'clips': playlist['clips'],
-                            # 'position': random.randrange(len(playlist['clips'])),
-                            'position': playlist_pos,
-                            'name': playlist['name'],
-                            'tags': playlist['tags'],
-                        }))
+                if prev_grid_list[i].get('playlist') is None:
+                # add this to deal with the absence of "playlist" data in old grid event.
+                # If there's no playlist data recorded, add the nextClip pool to nextPlaylist pool.
+                    next_playlist_index.append(next_clip_index)
+                    break
+                else:
+                # if "playlist" and "playlistPostion" (if not, default to 0) exists in grid event
+                    for playlist in self.playlists:
+                        if playlist.get('name')== prev_grid_list[i].get('playlist'):
+                            if len(playlist["clips"]) == 1:
+                                next_playlist_index.append(i)
+                                break
+                            # Discuss how this behavour should be: should it switch to a new playlist if it is the end of the playlist clip sequence already?
+                            elif prev_grid_list[i].get('playlistPosition', 0) + 1 == len(playlist['clips']):
+                                playlist_pos = 0
+                            else:
+                                playlist_pos = prev_grid_list[i].get('playlistPosition', 0) + 1
+                            
+                            rec_list.append((i, {
+                                'clips': playlist['clips'],
+                                # 'position': random.randrange(len(playlist['clips'])),
+                                'position': playlist_pos,
+                                'name': playlist['name'],
+                                'tags': playlist['tags'],
+                            }))
 
             # randomly select playlists (excluding the playlists from the current grid once "playlist" is recorded for grid events)
             # for nextPlaylist pool.
             vids_exclude = [e.get("playlist") for e in prev_grid_list]
+            while None in vids_exclude:
+                vids_exclude.remove(None)
             video = self.get_recommendations(user, vids_exclude)
             rec_list += [(i, video[i]) for i in next_playlist_index]