bug: validateSync() fails on modelless documents

[captaincaius]

Do you want to request a feature or report a bug?

bug

What is the current behavior?

relates to #8237 - now you can create a document, but you can't validate it.

If the current behavior is a bug, please provide the steps to reproduce.

> const goose = require('./index.js');
undefined
> const schemo = new goose.Schema({num: {type: Number, default: 4}});
undefined
> const dokk = new goose.Document({}, schemo);
undefined
> dokk
{ num: 4 }
> dokk.validateSync();
TypeError: _this.constructor.emit is not a function
    at Document.validateSync (/home/captainlocal/dev/mongooseygoose/mongoose/lib/document.js:2347:21)
> 

What is the expected behavior?

validateSync() works as expected

What are the versions of Node.js, Mongoose and MongoDB you are using? Note that "latest" is not a version.
node 10, mongoose master