Documents with Defaults and Required causes error on save

[Kirk Sefchik]

When I set both default and required on a schema, saving a model causes an error if the model was instantiated using default values. 

For example: 

const Todo = new Schema({
  text: {
    type: String,
    required: true,
    default: '',
  },
  done: {
    type: Boolean,
    required: true,
    default: false,
  },
});

export default mongoose.model('Todo', Todo);

Later...

  new Todo()
  .save()
  .then(newTodo => res.json(newTodo))
  .catch(e => res.status(500).send(e));

Causes this error to be thrown:

{
    "errors": {
        "text": {
            "message": "Path `text` is required.",
            "name": "ValidatorError",
            "properties": {
                "type": "required",
                "message": "Path `{PATH}` is required.",
                "path": "text",
                "value": ""
            },
            "kind": "required",
            "path": "text",
            "value": ""
        }
    },
    "_message": "Todo validation failed",
    "name": "ValidationError"
}

Additionally, I can inspect the value of the created todo before I save it and I can see that it's properly populating. However Mongoose still won't let me save. :(\

  let todo = new Todo();
  console.log(todo.inspect());
  // { _id: 594972eefe0b873338fe939d, done: false, text: '' }
  // It's populated! Why won't it save?

  todo
  .save()
  .then(newTodo => res.json(newTodo))
  .catch(e => res.status(500).send(e));

TBH, this looks like a bug to me. There might be a way to do this that I'm not seeing... Anyone have any thoughts on how I can make this `save()` call work with default data?