fix: handle TypeError exposed by simple history logic (#5476)

Author: matthewelwell

api/core/models.py

@@ -83,8 +83,11 @@ class _BaseHistoricalModel(models.Model):
     class Meta:
         abstract = True
 
-    def get_change_details(self) -> typing.Optional[typing.List[ModelChange]]:  # type: ignore[return]
-        if self.history_type == "~":  # type: ignore[attr-defined]
+    def get_change_details(self) -> typing.List[ModelChange]:
+        # Note that self.prev_record should never be None when self.history_type == "~" but we have
+        # seen rare cases in Sentry which cause an unhandled exception, so we instead handle the case
+        # and fall back to just return an empty list.
+        if self.history_type == "~" and self.prev_record is not None:  # type: ignore[attr-defined]
             return [
                 change
                 for change in self.diff_against(self.prev_record).changes  # type: ignore[attr-defined]
@@ -96,11 +99,10 @@ def get_change_details(self) -> typing.Optional[typing.List[ModelChange]]:  # ty
                 for key, value in self.instance.to_dict().items()  # type: ignore[attr-defined]
                 if key not in self._change_details_excluded_fields  # type: ignore[attr-defined]
             ]
-        elif self.history_type == "-":  # type: ignore[attr-defined]
-            # Ignore deletes because they get painful due to cascade deletes
-            # Maybe we can resolve this in the future but for now it's not
-            # critical.
-            return []
+
+        # Note that we ignore deletes because they get painful due to cascade deletes. Maybe we can
+        # resolve this in the future but for now it's not critical.
+        return []
 
 
 def base_historical_model_factory(

api/features/serializers.py

@@ -567,7 +567,7 @@ def validate(self, attrs):  # type: ignore[no-untyped-def]
             )
 
         mv_values = attrs.get("multivariate_feature_state_values", [])
-        if sum([v["percentage_allocation"] for v in mv_values]) > 100:
+        if sum([v.get("percentage_allocation", 0) for v in mv_values]) > 100:
             raise serializers.ValidationError(
                 "Multivariate percentage values exceed 100%."
             )