null values are discarded from OpenAPI examples

[WilliamDEdwards]

First Check

• I added a very descriptive title to this issue.
• I used the GitHub search to find a similar issue and didn't find it.
• I searched the FastAPI documentation, with the integrated search.
• I already searched in Google "How to X in FastAPI" and didn't find any information.
• I already read and followed all the tutorial in the docs and didn't find an answer.
• I already checked if it is not related to FastAPI but to Pydantic.
• I already checked if it is not related to FastAPI but to Swagger UI.
• I already checked if it is not related to FastAPI but to ReDoc.

Commit to Help

• I commit to help with one of those options 👆

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

[WilliamDEdwards]

Over a year later, coming across my own issue... Which has been converted into a discussion?!

With Pydantic 2.x, there's a clear differentiation between required and optional. This causes my OpenAPI examples to be incorrect, because null values are omitted for required fields.

[cohml]

Bump. I'm experiencing the same and it's a headache. A required parameter with null as an acceptable value is not the same as an optional parameter.

This should be rectified, given the obvious interest on this discussion and the issue that spawned it. Or at the very least, implement a mechanism whereby developers can toggle whether or not display null parameters via the examples.