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

packages/serialization/json/kiota_serialization_json/json_parse_node.py

@@ -185,6 +185,8 @@ def get_enum_value(self, enum_class: K) -> Optional[K]:
         Returns:
             Optional[K]: The enum value of the node
         """
+        if self._json_node is None:
+            return None
         raw_key = str(self._json_node)
         if not raw_key:
             return None

packages/serialization/json/tests/unit/test_nullable_enum.py

@@ -0,0 +1,28 @@
+import json
+from enum import Enum
+
+import pytest
+
+from kiota_serialization_json.json_parse_node import JsonParseNode
+
+
+class RiskLevel(Enum):
+    None_ = 'none'
+    Low = 'low'
+
+
+@pytest.mark.parametrize(
+    'payload, expected', [
+        ('null', None),
+        ('"none"', RiskLevel.None_),
+        ('"low"', RiskLevel.Low),
+    ]
+)
+def test_nullable_enum_distinguishes_null_from_none_member(payload, expected):
+    node = JsonParseNode(json.loads(payload))
+    assert node.get_enum_value(RiskLevel) is expected
+
+
+def test_nullable_enum_collection_preserves_null_entries():
+    node = JsonParseNode(json.loads('["none", null, "low"]'))
+    assert node.get_collection_of_enum_values(RiskLevel) == [RiskLevel.None_, None, RiskLevel.Low]