fix(event-handler): return dict on missing multi_value_headers (#3824)

* fix(parameters): make cache aware of single vs multiple calls

Signed-off-by: heitorlessa <lessa@amazon.co.uk>

* chore: cleanup, add test for single and nested

Signed-off-by: heitorlessa <lessa@amazon.co.uk>

* fix(event-handler): return dict on missing multi_value_headers

Signed-off-by: heitorlessa <lessa@amazon.co.uk>

* chore: default dict for multi query strings too

Signed-off-by: heitorlessa <lessa@amazon.co.uk>

* revert: path_parameters and stage_variables unrelated to the issue

---------

Signed-off-by: heitorlessa <lessa@amazon.co.uk>

Author: heitorlessa

aws_lambda_powertools/utilities/data_classes/api_gateway_proxy_event.py

@@ -112,11 +112,11 @@ def resource(self) -> str:
 
     @property
     def multi_value_headers(self) -> Dict[str, List[str]]:
-        return self["multiValueHeaders"]
+        return self.get("multiValueHeaders") or {}
 
     @property
-    def multi_value_query_string_parameters(self) -> Optional[Dict[str, List[str]]]:
-        return self.get("multiValueQueryStringParameters")
+    def multi_value_query_string_parameters(self) -> Dict[str, List[str]]:
+        return self.get("multiValueQueryStringParameters") or {}
 
     @property
     def resolved_query_string_parameters(self) -> Dict[str, List[str]]:

tests/functional/event_handler/test_openapi_validation_middleware.py

@@ -1108,3 +1108,23 @@ def my_path(
     # THEN the handler should be invoked and return 200
     result = app(gw_event_http, {})
     assert result["statusCode"] == 200
+
+
+def test_validate_with_minimal_event():
+    # GIVEN an APIGatewayRestResolver with validation enabled
+    app = APIGatewayRestResolver(enable_validation=True)
+
+    # WHEN a handler is defined with a default scalar parameter
+    @app.get("/users/<user_id>")
+    def handler(user_id: int = 123):
+        print(user_id)
+
+    minimal_event = {
+        "path": "/users/123",
+        "httpMethod": "GET",
+        "requestContext": {"requestId": "227b78aa-779d-47d4-a48e-ce62120393b8"},  # correlation ID
+    }
+
+    # THEN the handler should be invoked and return 200
+    result = app(minimal_event, {})
+    assert result["statusCode"] == 200