Model property not optional when referencing a nullable subschema

[grant-zietsman]

Describe the bug

Given an OpenAPI component schema configured with nullable: true, properties referencing this schema are not generated as optional.

To Reproduce

Example schema (OpenAPI):

openapi: 3.0.3
components:
  schemas:
    Parent:
      type: object
      required:
        - child
      properties:
        child:
          $ref: "#/components/schemas/Child"
    Child:
      nullable: true
      type: object
      required:
        - value
      properties:
        value:
          type: string

Used commandline:

datamodel-code-generator datamodel-codegen \
    --input ... \
    --input-file-type openapi \
    --output-model-type typing.TypedDict \
    --target-python-version 3.12 \
    --strict-nullable \
    --use-annotated \
    --use-field-description \
    --use-schema-description \
    --use-standard-collections \
    --use-union-operator \
    --disable-timestamp

Model output

# generated by datamodel-codegen:
#   filename:  openapi.yaml

from __future__ import annotations

from typing import TypedDict


class Child(TypedDict):
    value: str


class Parent(TypedDict):
    child: Child

Expected behavior
It is expected that the child property of the Parent model be optional.

Model output

# generated by datamodel-codegen:
#   filename:  openapi.yaml

from __future__ import annotations

from typing import TypedDict


class Child(TypedDict):
    value: str


class Parent(TypedDict):
    child: Child | None

Version:

• OS: iOS 15.1.1
• Python version: 3.12.4
• datamodel-code-generator version: 0.26.4