Describe the bug
For some reason, all of my fields are set as nullable, using strict-nullable dosen't change anything. This migh well be my error, but after spending much time trying endless combinations of settings, I resorted to opening a bug report.
To Reproduce

Example schema:

openapi: 3.0.0
components:
  schemas:
    ParentCompany:
      description: A parent company record
      type: object
      properties:
        id:
          type: integer
          nullable: true
        name:
          type: string

Used commandline:

$ datamodel-codegen --input ./src/tvdb/swagger.yml --input-file-type openapi --output ./src/tvdb/generated_models.py --output-model-type pydantic_v2.BaseModel

pyprohect.toml:

[tool.datamodel-codegen]
field-constraints = true
snake-case-field = true
target-python-version = "3.12"
use-default-kwarg = true
use-exact-imports = true
use-field-description = true
use-union-operator = true
reuse-model = true
output-model-type = "pydantic_v2.BaseModel"
custom-file-header = "# ruff: noqa: D101 # Allow missing docstrings"
field-include-all-keys = true
strict-nullable = false # or true, dosen't change anything

Expected output

# ruff: noqa: D101 # Allow missing docstrings

from __future__ import annotations

from pydantic import BaseModel


class ParentCompany(BaseModel):
    id: int | None = None
    name: str

Actual output

# ruff: noqa: D101 # Allow missing docstrings

from __future__ import annotations

from pydantic import BaseModel


class ParentCompany(BaseModel):
    id: int | None = None
    name: str | None = None

Version:

• OS: windows 11
• Python version: 3.12
• datamodel-code-generator version: 0.25.8