"validation errors for OpenAPI" when requesting /docs

Describe the bug
I followed the example in https://tortoise.github.io/examples/fastapi.html#basic-non-relational-example, and when running the app and requesting '/docs', I get a "Fetch error: Internal Server Error /openapi.json"

To Reproduce
https://tortoise.github.io/examples/fastapi.html#basic-non-relational-example

Expected behavior
No errors.

Additional context
Traceback:

Traceback (most recent call last):
  ...
    return jsonable_encoder(OpenAPI(**output), by_alias=True, exclude_none=True)  # type: ignore
  File "pydantic/main.py", line 341, in pydantic.main.BaseModel.__init__
pydantic.error_wrappers.ValidationError: 2 validation errors for OpenAPI
components -> schemas -> models.user.User.leaf -> additionalProperties
  value is not a valid dict (type=type_error.dict)
components -> schemas -> models.user.User.leaf -> $ref
  field required (type=value_error.missing)

Reproduce the failure with the FastAPI basic non-relational example linked in the issue and request /docs, then inspect the generated /openapi.json around the models.user.User.leaf schema. Done means the example serves its OpenAPI document without the reported Pydantic validation errors.