[Python] How do I correctly nest Pydantic models in a FastAPI response?

The example code is below. Seems like when I nest two models, the nested models don't show up in the response even though the app can prove that the data is there. See the example below.

Feels like I'm just doing something fundamentally wrong, but this doesn't seem like a wrong pattern to adopt, especially when the other parts seem to be just fine as is.

#!/usr/bin/env python3

from fastapi import FastAPI
from pydantic import BaseModel

class APIResponse(BaseModel):
status: str
data: BaseModel | None = None

class APIData(BaseModel):
name: str
count: int

app = FastAPI()
@app.get('/')
async def get_root():
data = APIData(name="foo", count=1)
response = APIResponse(status="success", data=data)

print(data)
''' name='foo' count=1 '''
print(response)
''' status='success' data=APIData(name='foo', count=1) '''

return data
''' Returns {"name":"name_value","count":1} '''

return response
'''
Expected {"status": "success", "data": {"name":"foo","count":1}}
Actual {"status":"success","data":{}}
'''

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