For example, if you have a model like:

                ```python
                from pydantic import BaseModel

                class Item(BaseModel):
                    name: str
                    tags: list[str] = []
                ```

                When `Item` is used for input, a request body, `tags` is not required,

```Python
from fastapi import FastAPI
from pydantic import BaseModel as BaseModelV2
from pydantic.v1 import BaseModel


class Item(BaseModel):
    name: str
    description: str | None = None


class ItemV2(BaseModelV2):
    title: str
    summary: str | None = None


app = FastAPI()