Panic when attempting to refer to an external schema

[harryjph]

My API is returning a JSON schema, and I'm trying to tell my OpenAPI clients that this is the case by referring to the well-known schema URL https://json-schema.org/draft/2020-12/schema.

I just want my openapi.json to contain something like:

"responses": {
  "200": {
     "content": {
       "application/json": {
         "schema": {
           "$ref": "https://json-schema.org/draft/2020-12/schema"
         }
       }
     },
   },

I've attempted to do that like this (full example here):

Responses: map[string]*huma.Response{
    "200": {
        Content: map[string]*huma.MediaType{
            "application/json": {
                Schema: &huma.Schema{
                    Ref: "https://json-schema.org/draft/2020-12/schema",
                },
            },
        },
    },
},

But this produces a panic:

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x8 pc=0x5c353c]

goroutine 1 [running]:
github.com/danielgtaylor/huma/v2.(*SchemaLinkTransformer).addSchemaField(0xc00011ae70, 0xc00012e210, 0xc00011aff0)
	/tmp/gopath2575097088/pkg/mod/github.com/danielgtaylor/huma/[email protected]/transforms.go:57 +0x7c
github.com/danielgtaylor/huma/v2.(*SchemaLinkTransformer).OnAddOperation(0xc00011ae70, 0xc00012e210, 0xc00015f2c0)
	/tmp/gopath2575097088/pkg/mod/github.com/danielgtaylor/huma/[email protected]/transforms.go:103 +0x23d
github.com/danielgtaylor/huma/v2.(*OpenAPI).AddOperation(0xc00012e210, 0xc00015f2c0)
	/tmp/gopath2575097088/pkg/mod/github.com/danielgtaylor/huma/[email protected]/openapi.go:1533 +0x306
github.com/danielgtaylor/huma/v2.Register[...]({_, _}, {{0x64ae2c, 0x3}, {0x64ad38, 0x1}, 0x0, 0x0, 0x0, {0x0, ...}, ...}, ...)
	/tmp/gopath2575097088/pkg/mod/github.com/danielgtaylor/huma/[email protected]/huma.go:893 +0x2405
main.main()
	/tmp/sandbox4189181463/prog.go:14 +0x2f6

This occurs because the schema variable returned here isn't nil-checked before it is accessed on the following line.

Is this the correct way to accomplish this and this is a bug? Or am I doing something wrong?