fix(json): distinguish null from the none enum member

[Shubham Padkonde (Shubham-Padkonde)]

Overview

Preserve JSON null when parsing an enum that has a None_ = "none" member. Currently str(None) becomes "None", which takes the reserved-keyword handling path and returns the actual enum member. A missing value can therefore be mistaken for an explicitly supplied "none" value.

Return None before converting a null node to text. The wire value "none" still resolves to None_, and ordinary enum values are unchanged. Collection entries use the same correction.

Related Issue

No separate issue found. The regression is reproduced by JsonParseNode(None).get_enum_value() with an enum containing None_ = "none".

Testing Instructions

• Install the local abstractions and JSON serialization packages and the JSON package's test dependencies.
• From packages/serialization/json, run python -m pytest tests -q: all 200 tests pass.
• The scalar-null and null-collection-entry regressions both fail before the fix; explicit "none" and "low" remain valid.
• Mypy passes for all six source files; YAPF reports no changes for the edited source and new tests.

Pylint rates the source 10/10 but reports the existing suggestion-mode configuration option as unrecognized in the installed version.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[Vincent Biret (baywet)]

Thanks for the contribution!

[Copilot]

Copilot review overview

🟢 Approval recommended

The localized fix preserves non-null behavior and includes focused regression coverage with no unresolved findings.

Review effort: Balanced
Findings: None

What changed in this PR

Fixes JSON enum parsing so null remains Python None rather than resolving to the enum member None_.

Changes:

• Returns early for null nodes, preserving non-null behavior.
• Adds scalar and collection regression tests.

File	Description
packages/​serialization/​json/​tests/​unit/​test_nullable_enum.py	Tests null entries and explicit enum values.
packages/​serialization/​json/​kiota_serialization_json/​json_parse_node.py	Handles null before converting enum values to text.

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