From 4ff8c57ba4620a8737e666419b2d55dcf7a8e220 Mon Sep 17 00:00:00 2001
From: Koudai Aono <koxudaxi@gmail.com>
Date: Sat, 20 Dec 2025 14:45:06 +0000
Subject: [PATCH] Fix nullable field access in custom templates with
 strict_nullable

---
 .../parser/jsonschema.py                      | 14 ++++++---
 .../parser/openapi.py                         | 10 +++++--
 tests/parser/test_openapi.py                  | 29 +++++++++++++++++++
 3 files changed, 47 insertions(+), 6 deletions(-)

diff --git a/src/datamodel_code_generator/parser/jsonschema.py b/src/datamodel_code_generator/parser/jsonschema.py
index 1834937b9..b816ce07d 100644
--- a/src/datamodel_code_generator/parser/jsonschema.py
+++ b/src/datamodel_code_generator/parser/jsonschema.py
@@ -335,7 +335,7 @@ def validate_null_type(cls, value: Any) -> Any:  # noqa: N805
     properties: Optional[dict[str, Union[JsonSchemaObject, bool]]] = None  # noqa: UP007, UP045
     required: list[str] = []  # noqa: RUF012
     ref: Optional[str] = Field(default=None, alias="$ref")  # noqa: UP045
-    nullable: Optional[bool] = False  # noqa: UP045
+    nullable: Optional[bool] = None  # noqa: UP045
     x_enum_varnames: list[str] = Field(default_factory=list, alias="x-enum-varnames")
     x_enum_names: list[str] = Field(default_factory=list, alias="x-enumNames")
     description: Optional[str] = None  # noqa: UP045
@@ -1032,7 +1032,9 @@ def get_object_field(  # noqa: PLR0913
             required=required,
             alias=alias,
             constraints=constraints,
-            nullable=field.nullable if self.strict_nullable and (field.has_default or required) else None,
+            nullable=field.nullable
+            if self.strict_nullable and field.nullable is not None
+            else (False if self.strict_nullable and (field.has_default or required) else None),
             strip_default_none=self.strip_default_none,
             extras=self.get_field_extras(field),
             use_annotated=self.use_annotated,
@@ -1075,7 +1077,9 @@ def get_ref_data_type(self, ref: str) -> DataType:
         reference = self.model_resolver.add_ref(ref)
         ref_schema = self._load_ref_schema_object(ref)
         is_optional = (
-            ref_schema.type_has_null or ref_schema.type == "null" or (self.strict_nullable and ref_schema.nullable)
+            ref_schema.type_has_null
+            or ref_schema.type == "null"
+            or (self.strict_nullable and ref_schema.nullable is True)
         )
         return self.data_type(reference=reference, is_optional=is_optional)
 
@@ -2576,7 +2580,9 @@ def parse_root_type(  # noqa: PLR0912
                     default=obj.default,
                     required=required,
                     constraints=obj.dict() if self.field_constraints else {},
-                    nullable=obj.nullable if self.strict_nullable else None,
+                    nullable=obj.nullable
+                    if self.strict_nullable and obj.nullable is not None
+                    else (False if self.strict_nullable and obj.has_default else None),
                     strip_default_none=self.strip_default_none,
                     extras=self.get_field_extras(obj),
                     use_annotated=self.use_annotated,
diff --git a/src/datamodel_code_generator/parser/openapi.py b/src/datamodel_code_generator/parser/openapi.py
index cef0fbddb..58ad5cf76 100644
--- a/src/datamodel_code_generator/parser/openapi.py
+++ b/src/datamodel_code_generator/parser/openapi.py
@@ -671,8 +671,14 @@ def parse_all_parameters(
                         if object_schema and self.is_constraints_field(object_schema)
                         else None,
                         nullable=object_schema.nullable
-                        if object_schema and self.strict_nullable and (object_schema.has_default or parameter.required)
-                        else None,
+                        if object_schema and self.strict_nullable and object_schema.nullable is not None
+                        else (
+                            False
+                            if object_schema
+                            and self.strict_nullable
+                            and (object_schema.has_default or parameter.required)
+                            else None
+                        ),
                         strip_default_none=self.strip_default_none,
                         extras=self.get_field_extras(object_schema) if object_schema else {},
                         use_annotated=self.use_annotated,
diff --git a/tests/parser/test_openapi.py b/tests/parser/test_openapi.py
index 2df603c9a..f25c601ae 100644
--- a/tests/parser/test_openapi.py
+++ b/tests/parser/test_openapi.py
@@ -946,3 +946,32 @@ def test_parse_responses_return(
         for content_type, expected_type_hint in expected_content_types.items():
             assert content_type in result[status_code]
             assert result[status_code][content_type].type_hint == expected_type_hint
+
+
+def test_parse_all_parameters_strict_nullable() -> None:
+    """Test that strict_nullable exposes nullable for optional parameters without default."""
+    parser = OpenAPIParser(
+        data_model_field_type=DataModelField,
+        source="",
+        openapi_scopes=[OpenAPIScope.Parameters],
+        strict_nullable=True,
+    )
+    parameters_data = [
+        {"name": "nullable_param", "in": "query", "required": False, "schema": {"type": "string", "nullable": True}},
+        {
+            "name": "non_nullable_param",
+            "in": "query",
+            "required": False,
+            "schema": {"type": "string", "nullable": False},
+        },
+    ]
+    result = parser.parse_all_parameters(
+        "TestParametersQuery",
+        [ParameterObject.parse_obj(param_data) for param_data in parameters_data],
+        ["test", "path"],
+    )
+    assert result is not None
+    fields = parser.results[0].fields
+    assert len(fields) == 2
+    assert fields[0].nullable is True
+    assert fields[1].nullable is False