Move null environment check to object-level validate()

Field-level validate_environment was blocking the context fallback
in validate() from ever running. Now validate_environment just guards
the .id access, and validate() resolves environment from context
before rejecting null.

Author: wavebyrd

api/features/serializers.py

@@ -597,16 +597,18 @@ def validate_feature(self, feature):  # type: ignore[no-untyped-def]
         return feature
 
     def validate_environment(self, environment):  # type: ignore[no-untyped-def]
-        if environment is None:
-            raise serializers.ValidationError("This field may not be null.")
-        if self.instance and self.instance.environment_id != environment.id:  # type: ignore[union-attr]
+        if environment is not None and self.instance and self.instance.environment_id != environment.id:  # type: ignore[union-attr]
             raise serializers.ValidationError(
                 "Cannot change the environment of a feature state"
             )
         return environment
 
     def validate(self, attrs):  # type: ignore[no-untyped-def]
-        environment = attrs.get("environment") or self.context["environment"]
+        environment = attrs.get("environment") or self.context.get("environment")
+        if environment is None:
+            raise serializers.ValidationError(
+                {"environment": ["This field may not be null."]}
+            )
         identity = attrs.get("identity")
         feature_segment = attrs.get("feature_segment")
         identifier = attrs.pop("identifier", None)

api/tests/unit/features/test_unit_features_serializers.py

@@ -14,10 +14,10 @@
 from features.serializers import FeatureStateSerializerBasic
 
 
-def test_feature_state_serializer_basic__null_environment__returns_validation_error(  # type: ignore[no-untyped-def]
+def test_feature_state_serializer_basic__null_environment_no_context__returns_validation_error(  # type: ignore[no-untyped-def]
     feature, environment
 ):
-    # Given
+    # Given - null environment in payload and no environment in context
     feature_state = FeatureState.objects.get(feature=feature, environment=environment)
     data = {
         "id": feature_state.id,
@@ -27,7 +27,7 @@ def test_feature_state_serializer_basic__null_environment__returns_validation_er
     serializer = FeatureStateSerializerBasic(
         instance=feature_state,
         data=data,
-        context={"environment": environment},
+        context={},
     )
 
     # When
@@ -38,6 +38,29 @@ def test_feature_state_serializer_basic__null_environment__returns_validation_er
     assert "environment" in serializer.errors
 
 
+def test_feature_state_serializer_basic__null_environment_with_context__falls_back_to_context(  # type: ignore[no-untyped-def]
+    feature, environment
+):
+    # Given - null environment in payload but valid environment in context
+    feature_state = FeatureState.objects.get(feature=feature, environment=environment)
+    data = {
+        "id": feature_state.id,
+        "feature": feature.id,
+        "environment": None,
+    }
+    serializer = FeatureStateSerializerBasic(
+        instance=feature_state,
+        data=data,
+        context={"environment": environment},
+    )
+
+    # When
+    is_valid = serializer.is_valid()
+
+    # Then - should fall back to context environment
+    assert is_valid
+
+
 @pytest.mark.parametrize(
     "percentage_value, expected_is_valid", ((90, True), (100, True), (110, False))
 )