Regression - .env nested optional model support

[slingshotvfx]

As of v2.5.0, the following code fails:

# .env
not_nested=works
NESTED__A=fails
NESTED__b=2

import os

from pydantic import BaseModel
from pydantic_settings import BaseSettings, SettingsConfigDict


class NestedSettings(BaseModel):
    A: str
    b: int

class Settings(BaseSettings):
    not_nested: str
    NESTED: NestedSettings | None

    model_config = SettingsConfigDict(
        env_file=".env",
        env_nested_delimiter="__",
        extra="forbid",
    )

print(Settings())

result:

pydantic_core._pydantic_core.ValidationError: 2 validation errors for Settings
nested__a
  Extra inputs are not permitted [type=extra_forbidden, input_value='fails', input_type=str]
    For further information visit https://errors.pydantic.dev/2.9/v/extra_forbidden
nested__b
  Extra inputs are not permitted [type=extra_forbidden, input_value='2', input_type=str]
    For further information visit https://errors.pydantic.dev/2.9/v/extra_forbidden

setting extra="allow" ends up with duplicate NESTED and nested__* fields on the model:

not_nested='works' NESTED=NestedSettings(A='fails', b=2) nested__a='fails' nested__b='2'

removing | None from NESTED: NestedSettings works as expected when forbid is both True or False:

not_nested='works' NESTED=NestedSettings(A='fails', b=2)

Using Python 3.12 on Windows 11. This worked as expected in 2.4.0

[hramezani]

Thanks @slingshotvfx for reporting this bug.

I will prepare a fix for it.

[hramezani]

I created #423 as a fix.

Could you please confirm the fix?

[slingshotvfx]

Confirmed #423 fixes the issue for me.

Thanks!

[hramezani]

Thanks @slingshotvfx for checking!

Fixed in f3a25f2