Debug stupidity

submissions/forms.py

@@ -640,6 +640,6 @@ class SubmissionCycleChoiceForm(forms.ModelForm):
     def __init__(self, *args, **kwargs):
         super().__init__(*args, **kwargs)
         self.fields['refereeing_cycle'].default = None
-        other_submission = self.instance.other_versions[0]
+        other_submission = self.instance.other_versions.first()
         if other_submission:
             self.fields['referees_reinvite'].queryset = other_submission.referee_invitations.all()