[BUG] NoneType model value examples are not supported

Description

I’m not able to pass a None/ as an example for a model value created with pydantic.Field

Looks like parser can’t find a difference between example=None as a NoneType variable and “missing example field”

class SomeResponse(BaseModel):
       city: Optional[str] = Field(..., nullable=True, example=None)

Expected openapi.json

"city": {
"title": "City",
"type": "string",
"nullable": true,
"example": null
}

Occurred openapi.json

"city": {
"title": "City",
"type": "string",
"nullable": true
}

Environment

• OS: macOS

• FastAPI Version: 0.61.1

• pydantic Version: 1.6.1

• Python version: 3.7.9

[sommergis]

Hi all, I ran into the same issue today. It seems like None values of fields in examples in OpenAPI schema generation are being excluded by FastAPI. The API works as expected, it’s only an issue in the OpenAPI schema.

Sample Model

class APIErrorMessage(BaseModel):
    """ Model for basic API response for an unsuccessful request. """
    content: Any = None
    error: str = ""
    detail: Optional[str] = None

    class Config:
        """ Real world example for OpenAPI documentation """
        schema_extra = {
            "example": {
                "content": None,
                "error": "Authentication Error",
                "detail": "key validity expired"
            }
        }

OpenAPI Response

"example": {
    "error": "Authentication Error",
    "detail": "key validity expired"
}

Maybe this is the location in the code? exclude_none=True

https://github.com/tiangolo/fastapi/blob/d2eb4a71eef08e201082d23517d4ddc99ff258b5/fastapi/openapi/utils.py#L377

Environment

FastAPI Version: 0.62.0

[abuendia]

Hi @tiangolo - Could you please take a look at this?