Setting map on update with an Object throws an Error

[foldess]

Do you want to request a feature or report a bug?
Bug
What is the current behavior?
Creating an schema like:

const child = new mongoose.Schema(
    {
        name: {
            type: mongoose.Schema.Types.Map,
            of: String,
        }
    }
)

const parent = new mongoose.Schema(
    {
        children: {
            type: [child],
        }
    }
)
mongoose.model('Parent', parent)

And than trying to do an update of a single child like results in error

updateData = { name: {en: "en Name", it: "it Name"} }

Parent.findOneAndUpdate({ 'children._id': id }, { 'children.$.name': updateData.name }, { new: true })

OR

Parent.findOneAndUpdate({ 'children._id': id }, { $set { 'children.$.name': updateData.name } }, { new: true })

gives the following error:

Cast to string failed for value \"{ it: 'it Name', en: 'en Name' }\" (type Object) at path \"name.$*\"

Of course in my case parent an child have more attributes, and i want to update only the attributes that are passed that are present in the update data however if i just try to set the whole 'children.$' as updateData i lose already present data because i'm overwriting the whole sub Document

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

What is the expected behavior?
Update the sub Document wihout overwriting it as a whole

What are the versions of Node.js, Mongoose and MongoDB you are using? Note that "latest" is not a version.
node: 14.16.0
mongoose: 5.12.10
mongodb: 4.4.6

[foldess]

I wrote a temporary solution for this matter while i wait a response

let object = Object.keys(updateData).reduce((obj, item) => {
            if (typeof updateData[item] === 'object' && !Array.isArray(updateData[item])) {
                const key = 'children.$.' + item
                 Object.keys(updateData[item]).forEach((item2) => {
                    obj[key + '.' + item2] = updateData[item][item2]
                })
                return obj
            } else {
                obj['children.$.' + item] = updateData[item]
                return obj
            }
        }, {})

const update = await Parent.findOneAndUpdate({ 'children._id': id }, { ...object }, { new: true })

[IslandRhythms]

const mongoose = require('mongoose');

const child = new mongoose.Schema(
    {
        name: {
            type: mongoose.Schema.Types.Map,
            of: String,
        }
    }
)

const parent = new mongoose.Schema(
    {
        children: {
            type: [child],
        }
    }
)
const Parent = mongoose.model('Parent', parent)



async function run() {
    await mongoose.connect('mongodb://localhost:27017/test', {
        useNewUrlParser: true,
        useUnifiedTopology: true,
      });
    
    await mongoose.connection.dropDatabase();

   let entry = await Parent.create({
        children: [{name: {github: 'hello', twitter: 'world'}}]
    });
    console.log(entry);
    let newEntry = await Parent.findOneAndUpdate({ _id: entry._id }, { $set: { 'children.$.name': { fart:'boy' }} });
    console.log(newEntry.children[0]);
}
run();