Empty subject attributes in python are empty tuples instead of None

[bennettandrews]

We ran into an issue where we were dropping assignment events in our downstream logger due to unexpected subject attribute values. If a None value is passed into subject attributes, they come back as empty tuple in the AssignmentLogger such as user_id: () which does not conform to the expected type of subject_attributes: Dict[str, Union[str, int, float, bool, None]],.

We ended up adding:

return {
  k: None if v == () else v|
  for k, v in assignment_event.get("subjectAttributes", {}).items()
}

The issue seems to be in https://github.com/Eppo-exp/eppo-multiplatform/blob/main/eppo_core/src/pyo3.rs#L28. The rust Option<T> when None is converted back to python uses ().to_object(py) which will create an empty tuple object instead of py.None()

Example

Tested on eppo-sever-sdk 4.0.0 and 4.2.4

client = eppo_client.get_instance()
user = get_current_user()

variation = client.get_boolean_assignment(
    'show-new-feature',
    user.id,
    { 'country': None },
    False
)

With AssignmentLogger

class LocalAssignmentLogger(AssignmentLogger):
	def log_assignment(self, assignment_event: dict) -> None:
		subject_attributes = assignment_event.get("subjectAttributes", {})
		print(f"Subject attributes: {subject_attributes}")

Country comes back as ()

Subject attributes: {'country': () }