Type null does not work with Typebox

[Edgar200021]

Prerequisites

• I have written a descriptive issue title
• I have searched existing issues to ensure the bug has not already been reported

Fastify version

5.4.0

Plugin version

9.5.1

Node.js version

22

Operating system

Linux

Operating system version (i.e. 20.04, 11.3, 10)

Operating System: Arch Linux Kernel: Linux 6.15.6-arch1-1

Description

Hi, I'm using @fastify/type-provider-typebox to generate schemas, I noticed that when I pass type null, swagger doesn't understand this type

Generic type

import { type TSchema, Type } from "@sinclair/typebox";

export const SuccessResponseSchema = <T extends TSchema>(T: T) =>
	Type.Object({
		status: Type.Literal("success"),
		data: T,
	});

Usage in the function

import {
	type FastifyPluginAsyncTypebox,
	Type,
} from "@fastify/type-provider-typebox";
import { SignInSchema } from "../schemas/auth/sign-in.schema.js";
import {
	ErrorResponseSchema,
	SuccessResponseSchema,
	ValidationErrorResponseSchema,
} from "../schemas/base.js";

const plugin: FastifyPluginAsyncTypebox = async (fastify) => {
	fastify.post(
		"/auth/sign-up",
		{
			schema: {
				body: SignInSchema,
				response: {
					201: SuccessResponseSchema(Type.Null()),
					400: Type.Union([ErrorResponseSchema, ValidationErrorResponseSchema]),
				},
				tags: ["Authentication"],
			},
		},

The result

Link to code that reproduces the bug

Included in the description

Expected Behavior

The Type.Null() schema from TypeBox must be properly supported in the generated OpenAPI (Swagger) specification.

[climba03003]

Since Swagger and OpenAPI do not support { type: "null" } and you need to use { nullable: true }.
We cannot directly replace the it with nullable: true because it also requires to know the type.

[Edgar200021]

Since Swagger and OpenAPI do not support { type: "null" } and you need to use { nullable: true }. We cannot directly replace the it with nullable: true because it also requires to know the type.

I understand Typebox can't be used for this ? That is, where there is null in the data should be changed to such a scheme

201: {
   description: "Successful response",
   type: "object",
   properties: {
      data: { type: "string" }, 
      nullable: true,
   },
}

[khokm]

OpenAPI 3.1 introduces support for jsonschema's 'null' type.
Are you using openapi 2.x.x (aka swagger) / openapi 3.0.x? Switching to openapi: "3.1.0" may resolve the problem
(personally i don't use 3.1 cuz swagger-ui doesn't show references to schemas for some reason, showing them as inlined instead).