null values are discarded from OpenAPI examples

[WilliamDEdwards]

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Example Code

Taken from https://fastapi.tiangolo.com/advanced/additional-responses/

from fastapi import FastAPI

import json

app = FastAPI()

@app.get("/", responses={200: {"content": {"application/json": {"example": {"absent": None, "present": "value"}}}}})
def read_root():
    return {"absent": None, "present": "value"}

print(json.dumps(app.openapi()))

Description

• Add an example to the OpenAPI spec (using example or examples)
• Set the value to None
• The example is absent

The code above outputs:

{"openapi": "3.0.2", "info": {"title": "FastAPI", "version": "0.1.0"}, "paths": {"/": {"get": {"summary": "Read Root", "operationId": "read_root__get", "responses": {"200": {"description": "Successful Response", "content": {"application/json": {"schema": {}, "example": {"present": "value"}}}}}}}}}

As you can see, the absent example is absent.

Operating System

Linux

Operating System Details

No response

FastAPI Version

0.73.0

Python Version

3.8.9

Additional Context

openapi.utils.get_openapi has this line:

return jsonable_encoder(OpenAPI(**output), by_alias=True, exclude_none=True)  # type: ignore

exclude_none could cause the issue.

When setting it to True, OpenAPI generation fails with the following error:

n is null