Nullable combined with allOf issue

[bnowak]

Hello,

I've got an issue in my project (where we're using https://github.com/nelmio/NelmioApiDocBundle with OAS 3.1 version) connected to nullable enums.

Currently for OAS 3.1 version it's rendered to spec as:

'nullableEnumType' => [
    'allOf' => [
        ['$ref' => '#/components/schemas/ArticleType81'], // enum ref
        ['type' => 'null'],
    ]
],

but it's impossible to match both types at the same time. We're using https://github.com/opis/json-schema to validate API data responses against API model schema and it reports above issue.

In OAS version 3.0 there's nullable field and it's used properly:

'nullableEnumType' => [
    'nullable' => true,
    'allOf' => [
        ['$ref' => '#/components/schemas/ArticleType81'], // enum ref
    ],
],

I think for OAS 3.1 we should wrap such nullable-allOf schemas with additional oneOf level to be something like:

'nullableEnumType' => [
    'oneOf' => [
        [
          'allOf' => [
              ['$ref' => '#/components/schemas/ArticleType81'], // enum ref
          ],
        ],
        ['type' => 'null'],
    ]
],

It seems that could be more general issue - not only connected to enums. Also, proposed solution IMO seems to be general as well.

I'll test it shortly and will prepare PR for it.

[bnowak]

I'm closing it as the root cause was in Nelmio api doc bundle and was solved there.