langchain - 💡(How to fix) Fix AzureChatOpenAI._create_chat_result emits PydanticSerializationUnexpectedValue warnings for structured-output responses

import warnings
from typing import Literal

import openai
from pydantic import BaseModel, SecretStr

from langchain_openai import AzureChatOpenAI


class ModelOutput(BaseModel):
    output: str


class MockParsedMessage(openai.BaseModel):
    role: Literal["assistant"] = "assistant"
    content: str = '{"output": "Paris"}'
    parsed: None = None
    refusal: str | None = None


class MockChoice(openai.BaseModel):
    index: int = 0
    finish_reason: Literal["stop"] = "stop"
    message: MockParsedMessage


class MockChatCompletion(openai.BaseModel):
    id: str = "chatcmpl-1"
    object: str = "chat.completion"
    created: int = 0
    model: str = "gpt-4o-mini"
    choices: list[MockChoice]
    usage: dict[str, int] | None = None


parsed_response = ModelOutput(output="Paris")
response = MockChatCompletion.model_construct(
    choices=[
        MockChoice.model_construct(
            message=MockParsedMessage.model_construct(parsed=parsed_response)
        )
    ],
    usage={"prompt_tokens": 1, "completion_tokens": 1, "total_tokens": 2},
)

llm = AzureChatOpenAI(
    azure_deployment="gpt-4o-mini",
    api_version="2024-10-01-preview",
    azure_endpoint="https://example.openai.azure.com",
    api_key=SecretStr("test"),
)

with warnings.catch_warnings(record=True) as caught:
    warnings.simplefilter("always")
    llm._create_chat_result(response)

print(f"# warnings: {len(caught)}")
for w in caught:
    print(w.category.__name__, str(w.message))

---

# warnings: 1
UserWarning Pydantic serializer warnings:
  PydanticSerializationUnexpectedValue(Expected `none` - serialized value may not be as expected [field_name='parsed', input_value=ModelOutput(output='Paris'), input_type=ModelOutput])

---

System Information
------------------
> OS:  Darwin
> OS Version:  Darwin Kernel Version 25.5.0: Mon Apr 27 20:39:42 PDT 2026; root:xnu-12377.121.6~2/RELEASE_ARM64_T6031
> Python Version:  3.12.10 (main, May 22 2025, 01:38:44) [Clang 20.1.4 ]

Package Information
-------------------
> langchain_core: 1.4.0
> langchain: 1.3.1
> langsmith: 0.8.5
> langchain_openai: 1.2.2
> langchain_protocol: 0.0.14
> langchain_tests: 1.1.9
> langgraph_sdk: 0.3.3

Optional packages not installed
-------------------------------
> deepagents
> deepagents-cli

Other Dependencies
------------------
> httpx: 0.28.1
> jsonpatch: 1.33
> langgraph: 1.2.0
> numpy: 2.3.4
> openai: 2.32.0
> orjson: 3.11.6
> packaging: 25.0
> pydantic: 2.12.2
> pytest: 9.0.3
> pytest-asyncio: 1.3.0
> pytest-benchmark: 5.0.1
> pytest-codspeed: 4.1.1
> pytest-recording: 0.13.4
> pytest-socket: 0.7.0
> pyyaml: 6.0.3
> requests: 2.33.0
> requests-toolbelt: 1.0.0
> rich: 14.2.0
> syrupy: 5.1.0
> tenacity: 9.1.2
> tiktoken: 0.12.0
> typing-extensions: 4.15.0
> uuid-utils: 0.12.0
> vcrpy: 8.1.1
> wrapt: 1.17.3
> xxhash: 3.6.0
> zstandard: 0.25.0