fast-json-stringify: Failed building the serialization schema when it is a typebox object with an "any" type

🐛 Bug Report

When using a valid schema with a property define as an any kind of type, {} in json schema (without enforced type), fastify just crash

To Reproduce

Steps to reproduce the behavior:

Add a response schema with something like

{
  schema: {
    response: {
      200: {type: "object", properties: {foo: {}}}
    }
  }
}

note the absence of type for property foo

Expected behavior

A clear and concise description of what you expected to happen.

FastifyError [Error]: Failed building the serialization schema for GET: /foos, due to error undefined unsupported
,    at Boot.emit (events.js:327:22)
,    at Boot.<anonymous> (/project/node_modules/fastify/lib/route.js:280:19)
,    at Object.onceWrapper (events.js:421:28)
,    at /project/node_modules/avvio/boot.js:153:12
,    at /project/node_modules/avvio/plugin.js:269:7
,    at done (/project/node_modules/avvio/plugin.js:201:5)
,    at check (/project/node_modules/avvio/plugin.js:225:9)
,    at internal/process/task_queues.js:153:7
,    at AsyncResource.runInAsyncScope (async_hooks.js:186:9)
,    at AsyncResource.runMicrotask (internal/process/task_queues.js:150:8) {
,  code: 'FST_ERR_SCH_SERIALIZATION_BUILD',
,  statusCode: 500
,}

Ajv validation as input works fine, schema is valid, serialisation should be fine too.

Your Environment

• node version: 12 LTS
• fastify version: ^3.3.0
• os: Linux
• any other relevant information