From 0fc0c5219ca37dbd74cce7e7b66bfb9ea8276e3c Mon Sep 17 00:00:00 2001
From: LeSingh1 <sshaurya914@gmail.com>
Date: Tue, 14 Jul 2026 15:47:24 -0700
Subject: [PATCH] Python: Map NoneType to JSON Schema "null" instead of
 "object" in schema builder

KernelJsonSchemaBuilder omitted NoneType from TYPE_MAPPING, so
get_json_schema(type(None)) and any union of 3+ members containing None
(e.g. int | str | None) emitted {"type": "object"} for the None member
instead of the correct {"type": "null"}. These schemas mislead LLMs
during function calling / structured output. The two-member Optional[T]
path builds nullability separately and was already correct.

Add NoneType (and the "None"/"NoneType" string names used by
build_from_type_name) to TYPE_MAPPING, with regression tests.
---
 .../schema/kernel_json_schema_builder.py      |  3 +++
 .../tests/unit/schema/test_schema_builder.py  | 21 +++++++++++++++++++
 2 files changed, 24 insertions(+)

diff --git a/python/semantic_kernel/schema/kernel_json_schema_builder.py b/python/semantic_kernel/schema/kernel_json_schema_builder.py
index 5ec519b5b377..03b9e73fb473 100644
--- a/python/semantic_kernel/schema/kernel_json_schema_builder.py
+++ b/python/semantic_kernel/schema/kernel_json_schema_builder.py
@@ -18,6 +18,7 @@
     dict: "object",
     set: "array",
     tuple: "array",
+    type(None): "null",
     "int": "integer",
     "str": "string",
     "bool": "boolean",
@@ -28,6 +29,8 @@
     "tuple": "array",
     "object": "object",
     "array": "array",
+    "None": "null",
+    "NoneType": "null",
 }
 
 
diff --git a/python/tests/unit/schema/test_schema_builder.py b/python/tests/unit/schema/test_schema_builder.py
index 5d24a599c96c..91c521150a71 100644
--- a/python/tests/unit/schema/test_schema_builder.py
+++ b/python/tests/unit/schema/test_schema_builder.py
@@ -228,6 +228,27 @@ def test_build_optional():
     assert schema == {"type": ["integer", "null"]}
 
 
+def test_get_json_schema_none_type():
+    # NoneType maps to the JSON Schema "null" type, not "object".
+    assert KernelJsonSchemaBuilder.get_json_schema(type(None)) == {"type": "null"}
+
+
+def test_build_none_type():
+    assert KernelJsonSchemaBuilder.build(type(None)) == {"type": "null"}
+
+
+def test_build_union_with_none():
+    # A union of more than two members that includes None must represent the
+    # None member as {"type": "null"}, not {"type": "object"}.
+    schema = KernelJsonSchemaBuilder.build(Union[int, str, None])
+    assert schema == {"anyOf": [{"type": "integer"}, {"type": "string"}, {"type": "null"}]}
+
+
+def test_build_from_type_name_none():
+    assert KernelJsonSchemaBuilder.build_from_type_name("None") == {"type": "null"}
+    assert KernelJsonSchemaBuilder.build_from_type_name("NoneType") == {"type": "null"}
+
+
 def test_build_model_schema_for_many_types():
     schema = KernelJsonSchemaBuilder.build(MockModel)
     expected = """