Update custom widget

Django 3.1 updated ModelChoiceIterator behaviour

src/newsreader/news/core/forms.py

@@ -12,7 +12,14 @@ class RulesWidget(CheckboxSelectMultiple):
 
     def create_option(self, *args, **kwargs):
         option = super().create_option(*args, **kwargs)
-        instance = self.choices.queryset.get(pk=option["value"])
+
+        # see https://docs.djangoproject.com/en/3.1/releases/3.1/#id1
+        try:
+            pk = int(option["value"])
+        except TypeError:
+            pk = option["value"].value
+
+        instance = self.choices.queryset.get(pk=pk)
 
         if self.category and instance.category:
             option["selected"] = self.category.pk == instance.category.pk