fastapi: RecursionError from response model in 0.47.1

Describe the bug

FastAPI 0.47.1 will not be able to start due to a RecursionError when there is a circular reference among models. The issue seems to originate from https://github.com/tiangolo/fastapi/pull/889. This works fine in 0.46.0.

Environment

• OS: Windows
• FastAPI Version: 0.47.1
• Python version: 3.7.0

To Reproduce

from typing import Optional

from fastapi import FastAPI
from pydantic import BaseModel, Field


class Group(BaseModel):
    representative: Optional['Person'] = Field(None)


class Person(BaseModel):
    group: Optional[Group] = Field(None)


Group.update_forward_refs()


app = FastAPI()


@app.get('/group/{group_id}', response_model=Group)
def get_group(group_id):
    return []

Expected behavior

No exception

Actual output

Traceback (most recent call last):
  File "test.py", line 21, in <module>
    @app.get('/group/{group_id}', response_model=Group)
  File "D:\virtualenvs\test\lib\site-packages\fastapi\routing.py", line 494, in decorator
    callbacks=callbacks,
  File "D:\virtualenvs\test\lib\site-packages\fastapi\routing.py", line 438, in add_api_route
    callbacks=callbacks,
  File "D:\virtualenvs\test\lib\site-packages\fastapi\routing.py", line 275, in __init__
    ] = create_cloned_field(self.response_field)
  File "D:\virtualenvs\test\lib\site-packages\fastapi\utils.py", line 100, in create_cloned_field
    use_type.__fields__[f.name] = create_cloned_field(f)
  File "D:\virtualenvs\test\lib\site-packages\fastapi\utils.py", line 100, in create_cloned_field
    use_type.__fields__[f.name] = create_cloned_field(f)
  File "D:\virtualenvs\test\lib\site-packages\fastapi\utils.py", line 100, in create_cloned_field
    use_type.__fields__[f.name] = create_cloned_field(f)
  [Previous line repeated 981 more times]
  File "D:\virtualenvs\test\lib\site-packages\fastapi\utils.py", line 97, in create_cloned_field
    original_type.__name__, __config__=original_type.__config__
  File "D:\virtualenvs\test\lib\site-packages\pydantic\main.py", line 773, in create_model
    return type(model_name, (__base__,), namespace)
  File "D:\virtualenvs\test\lib\site-packages\pydantic\main.py", line 152, in __new__
    if issubclass(base, BaseModel) and base != BaseModel:
  File "D:\virtualenvs\test\lib\abc.py", line 143, in __subclasscheck__
    return _abc_subclasscheck(cls, subclass)
RecursionError: maximum recursion depth exceeded in comparison