regression: 5.4.11 rejects subdocument required:false if type is not explicitly Object

[autopulated]

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

What is the current behavior?
in 5.4.10 and below, this is accepted:

var testschema = new mongoose.Schema({
    subdoc:{
        required:false
    }
});

If the current behavior is a bug, please provide the steps to reproduce.
In 5.4.11, the above schema produces the error:
(stack:TypeError: Invalid value for schema path `subdoc.required` ...

Unless the subdocument type is explicitly set to Object:

var testschema = new mongoose.Schema({
    subdoc:{
       type: Object,
        required:false
    }
});

What is the expected behavior?
5.4.11 should continue to accept schemas which were accepted under 5.4.10

Please mention your node.js, mongoose and MongoDB version.
tested with node v10.15.0 amongst other v10 versions.

[vkarpov15]

The fact that this worked in Mongoose 5.4.10 is an accident more than anything, the testschema you defined actually creates subdoc.required as a path of type mixed as opposed to a property subdoc of type object that isn't required:

const assert = require('assert');
const mongoose = require('mongoose');
mongoose.set('debug', true);

const GITHUB_ISSUE = `gh7512`;
const connectionString = `mongodb://localhost:27017/${ GITHUB_ISSUE }`;
const { Schema } = mongoose;

run().then(() => console.log('done')).catch(error => console.error(error.stack));

async function run() {
  await mongoose.connect(connectionString);
  await mongoose.connection.dropDatabase();

  
  var testschema = new mongoose.Schema({
    subdoc:{
        required:false
    }
  });

  console.log(testschema.path('subdoc.required')); // This is a path in the schema!

  var testschema2 = new mongoose.Schema({
    subdoc:{
        type: Object,
        required:false
    }
  });

  console.log(testschema2.path('subdoc.required')); // undefined
}

So your schema needs a little work.

But since this check has caused so much confusion, it was probably too big a change for a patch release. Just make sure you structure your schemas correctly going forward, because the way you wrote testschema will likely break in 6.0 (see #7181, etc)