Using | breaks with partial streaming

[ahuang11]

• This is actually a bug report.

What Model are you using?

gpt-4o-mini

Describe the bug

Follow up on #661 since that was closed before it was fixed

When streaming with a |, it crashes with TypeError: type 'types.UnionType' is not subscriptable

To Reproduce

import instructor
from pydantic import BaseModel
from openai import OpenAI


class User(BaseModel):
    name: str
    age: int
    category: str | None

client = instructor.from_openai(OpenAI())

# Extract structured data from natural language
res = client.chat.completions.create_partial(
    model="gpt-4o-mini",
    response_model=User,
    messages=[{"role": "user", "content": "John Doe is 30 years old."}],
)
res

Expected behavior

Swapping to Union works, but I expect them both to work

import instructor
from pydantic import BaseModel
from openai import OpenAI


class User(BaseModel):
    name: str
    age: int
    category: Union[str, None]

client = instructor.from_openai(OpenAI())

# Extract structured data from natural language
res = client.chat.completions.create_partial(
    model="gpt-4o-mini",
    response_model=User,
    messages=[{"role": "user", "content": "John Doe is 30 years old."}],
)
res