Make sure Profile.ban_reason is either None or non-empty string

judge/admin/profile.py

@@ -153,6 +153,12 @@ def get_form(self, request, obj=None, **kwargs):
             )
         return form
 
+    def save_model(self, request, obj, form, change):
+        super().save_model(request, obj, form, change)
+        if form.changed_data and 'ban_reason' in form.changed_data and form.cleaned_data['ban_reason'] == '':
+            obj.ban_reason = None
+            obj.save()
+
 
 class UserAdmin(OldUserAdmin):
     def save_model(self, request, obj, form, change):

judge/models/profile.py

@@ -221,7 +221,7 @@ def is_new_user(self):
 
     @cached_property
     def is_banned(self):
-        return self.ban_reason and not self.user.is_active
+        return not self.user.is_active and self.ban_reason is not None
 
     def can_be_banned_by(self, staff):
         return self.user != staff and not self.user.is_superuser and staff.has_perm('judge.ban_user')
@@ -370,7 +370,7 @@ def ban_user(self, reason):
     ban_user.alters_data = True
 
     def unban_user(self):
-        self.ban_reason = ''
+        self.ban_reason = None
         self.display_rank = Profile._meta.get_field('display_rank').get_default()
         self.is_unlisted = False
         self.save(update_fields=['ban_reason', 'display_rank', 'is_unlisted'])