Bad reference does not fail compilation inside response

When using this invalid swagger guardrail generates an empty 404 response instead of failing.

```yaml
swagger: "2.0"
info:
title: "Example API"
version: "1.0.0"
host: "example.com"
basePath: "/api"
schemes:
- "http"

definitions:
SomeData:
type: object
required:
- message
properties:
message:
type: string

responses:
InternalServerError: #500
description: 'Internal Server Error'
schema:
$ref: "#/definitions/SomeData"

paths:
/endpoint:
get:
responses:
'200':
description: 'Successful operation'
schema:
$ref: '#/definitions/SomeData'
'404':
$ref: '#/responses/DoesNotExist'
```

and the bad generated code

```scala
// ...

case class endpointResponseOK(value: api.specification.definitions.SomeData) extends endpointResponse(StatusCodes.OK)
case object endpointResponseNotFound extends endpointResponse(StatusCodes.NotFound)

//...
```

I would expect it to fail saying that the reference was not found like in other situations.