Bug: Depends() and Request parameters with a None default are not resolved on Python 3.10 #8648

Expected Behaviour

A route or middleware parameter declared as d: Annotated[str, Depends(get_dep)] = None receives the resolved dependency, and request: Request = None receives the Request, on every supported Python version.

Current Behaviour

On Python 3.10 only, both parameters receive None. typing.get_type_hints on 3.10 wraps the annotation of a parameter whose default is None in Optional[...], so Annotated[str, Depends(...)] becomes Union[Annotated[str, Depends(...)], None]. _get_depends_from_annotation only checks get_origin(annotation) is Annotated, and _find_request_param_name only checks annotation is Request, so neither matches and the parameter falls back to its default. Python 3.11 stopped wrapping, which is why 3.11+ work. Present since Depends() shipped in v3.28.0.

Confirmed in real Lambda functions on python3.10 (layer and zip package) and locally with a 3.10 virtualenv.

Code snippet

from typing import Annotated
from aws_lambda_powertools.event_handler import APIGatewayRestResolver, Depends

app = APIGatewayRestResolver()

def get_region() -> str:
    return "eu-west-1"

@app.get("/my/path")
def handler(region: Annotated[str, Depends(get_region)] = None):
    return {"region": region}

# python 3.10: {"region": null}
# python 3.11+: {"region": "eu-west-1"}

Possible Solution

Unwrap Optional[X] / X | None before inspecting the annotation, in _get_depends_from_annotation, in the Request injection inside solve_dependencies, and in _find_request_param_name. A small helper _unwrap_optional that returns the single non-None arg of a Union covers all three. Tests with = None defaults fail on 3.10 today and pass with the change.

Steps to Reproduce

Run the snippet with Python 3.10 using tests/events/apiGatewayProxyEvent.json as the event.

Powertools for AWS Lambda (Python) version

latest

AWS Lambda function runtime

3.10

Packaging format used

Lambda Layers, PyPi

Debugging logs