v2.3.1; question mark is an invalid character too

SaveMyPlaylist.py

@@ -60,7 +60,7 @@ class SaveMyPlaylist:
     TITLE = 1
     VIDEO_ID = 2
 
-    ILLEGAL_CHARS = ['NUL', '\\', '/', ':', '*', '"', '<', '>', '|']
+    ILLEGAL_CHARS = ['NUL', '\\', '/', ':', '*', '"', '<', '>', '|', '?']
 
     def __init__(self, apiKey, playlistId):
         with open('version.json', 'r', encoding='utf-8') as f:

version.json

 {
     "version": {
-        "name": "v2.3.0",
-        "code": 8,
-        "date": "14.04.20"
+        "name": "v2.3.1",
+        "code": 9,
+        "date": "18.04.20"
     }
 }
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