OpenAPI Generator issue reproducing JSON

spec.json

{
    "openapi": "3.0.0",
    "info": {
        "title": "Test REST-API",
        "version": "1.0"
    },
    "servers": [
        {
            "url": "https://api.example.com/v1"
        }
    ],
    "paths": {
        "/somepets": {
            "get": {
                "summary": "Get some pets",
                "operationId": "test\\RestApi\\somepetsController::fetch_all",
                "responses": {
                    "812": {
                        "description": "Custom HTTP status"
                    }
                }
            }
        }
    }
}