Type of subdocument not inferred in toJSON() about mongoose HOT 2 OPEN

import { Schema, model, connect, connection } from 'mongoose';

import type { Model, Types } from 'mongoose';
// Subdocument definition
interface Names {
  _id: Types.ObjectId;
  firstName: string;
}
// Document definition
interface User {
  names: Names[];
}

// TMethodsAndOverrides
type UserDocumentProps = {
  names: Types.DocumentArray<Names>;
};
type UserModelType = Model<User, {}, UserDocumentProps>;

const userSchema = new Schema<User, UserModelType>(
  {
    names: [new Schema<Names>({ firstName: String })],
  },
  { timestamps: true },
);

// Create model
const UserModel = model<User, UserModelType>('User', userSchema);


async function run() {
  await connect('mongodb://localhost:27017');
  await connection.dropDatabase();
  await UserModel.create({
    names: [{ firstName: 'John'}]
  })
  const doc = await UserModel.findOne({});
  const jsonDoc = doc?.toJSON();
  // Type string
  console.log(jsonDoc?.names[0]?.firstName);
  const jsonNames = doc?.names[0]?.toJSON();
  // Type any
  console.log(jsonNames?.firstName);
  const name: string = jsonNames?.firstName;
  console.log('done');
}

run();

async function run() {
  await connect('mongodb://localhost:27017');
  await connection.dropDatabase();
  await UserModel.create({
    names: [{ firstName: 'John' }],
  });
  const doc = await UserModel.findOne({});
  const jsonDoc = doc?.toJSON();
  // Type 'string | undefined' is not assignable to type 'boolean'
  const test: boolean = jsonDoc?.names[0]?.firstName;
  const jsonNames = doc?.names[0]?.toJSON();
  // No error
  const name: boolean = jsonNames?.firstName;
  console.log('done');
}