500 when calling /api/v1/features/featurestates/{pk}/ with empty environment

[sentry]

Sentry Issue: FLAGSMITH-API-5GQ

AttributeError: 'NoneType' object has no attribute 'id'
(8 additional frame(s) were not displayed)
...
  File "features/serializers.py", line 578, in validate_environment
    if self.instance and self.instance.environment_id != environment.id:  # type: ignore[union-attr]