Special Fields Error Message

When i try to open the special fields add on, i get this message:
Debug info:
Anki 2.1.28 (7d8818f8) Python 3.8.0 Qt 5.15.0 PyQt 5.15.0
Platform: Windows 10
Flags: frz=True ao=True sv=1
Add-ons, last update check: 2020-07-21 08:55:18

Caught exception:
Traceback (most recent call last):
File “C:\Users\sarka\AppData\Roaming\Anki2\addons21\1102281552\dialog.py”, line 316, in onFields
FieldDialog(mw, fields, parent=self)
File “C:\Users\sarka\AppData\Roaming\Anki2\addons21\1102281552\dialog.py”, line 41, in init
self.form.buttonBox.button(
AttributeError: ‘NoneType’ object has no attribute ‘setAutoDefault’

It is the add on that is causing the problem, when I start using shift it works normally.