Nullable in OAS 3.1 rendered as "'null'" string instead of "null"

[mjpieters]

Nullable fields should be rendered as "type": ["fieldType", "null"], not ["fieldType", "'null'"].

The field converter currently includes quotes around null in the literal string value, see

apispec/src/apispec/ext/marshmallow/field_converter.py

Line 283 in 5cf763e

attributes["type"] = make_type_list(ret.get("type")) + ["'null'"]

which results in JSON like this:

          "created_at": {
            "type": [
              "string",
              "'null'"
            ],
            "format": "date-time",
            "readOnly": true
          },

or as YAML:

       created_at:
          type:
            - string
            - '''null'''
          format: date-time
          readOnly: true

While the type string should be a string (and not None in Python, null in JSON or YAML), the extra quotes there are an error.

To fix, please drop the extra quotes in the value:

                attributes["type"] = make_type_list(ret.get("type")) + ["null"] 

Also see

• Understanding JSON Schema: null
• this specific valid specification test in the OpenAPI specification repository.

[lafrech]

I can't remember precisely, but it is very possible that I'm the one who put those quotes and I did it on purpose, but I guess I was wrong.

Thanks for the fix.