Support of `null` for other referenced types

[Antreesy]

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Based on https://github.com/nextcloud/spreed/blob/e6d2969c3ce08f70d52375e703a7b4e9986e6110/lib/ResponseDefinitions.php:

Primitives converted correctly:

 * @psalm-type TalkBot = array{
 *     description: ?string,
 * }

"required": [
    "description",
],
"properties": {
    "description": {
        "type": "string",
        "nullable": true
    },

Bot: {
    description: string | null;
}

But the same doesn't happen to other psalm-types:

 * @psalm-type TalkThreadInfo = array{
 *      first: ?TalkChatMessage,
 * }

"required": [
    "first",
],
"properties": {
  "first": {
      "$ref": "#/components/schemas/ChatMessage",
      "nullable": true
  },

Actual behaviour

ThreadInfo: {
   first: components["schemas"]["ChatMessage"];
}

Expected behaviour

ThreadInfo: {
   first: components["schemas"]["ChatMessage"] | null;
}

As i found out, they changed handling of nullables in 3.1.0, so after some playing around: this JSON output would work as expected:

"first": {
  "oneOf": [
    { "$ref": "#/components/schemas/ChatMessage" },
    { "type": "null" }
  ]
},

[provokateurin]

Yeah, I think using $ref and nullable together was never correct, although one draft version once allowed it. I think the correct syntax is way more complex to read, but if that's the way then we must follow 🤷‍♀️

[provokateurin]

Seems like OAI/OpenAPI-Specification#1368 (comment) is the way to go in OAS <3.1. With #193 we'd be able to use proper JSON schema and use the "type": "null" thing.

[provokateurin]

@Antreesy please test #262. I checked the diff in server and it looks good, but you should verify that it fixes the issue you saw in Talk.

[Antreesy]

you should verify that it fixes the issue you saw in Talk.

Can't test the PR, but the output with nullable, allOf: [] resolves correctly. Thanks!

[provokateurin]

Releases as v1.8.1.