MongoDB client transforming Date and ObjectId into empty objects

[takameyer]

The following code ends up saving an empty object in the Atlas Collection:

   const document = {
      _id: new ObjectId(),
      createdAt: new Date(),
    };
    user
      .mongoClient('mongodb-atlas')
      .db('chat')
      .collection('messages')
      .insertOne(document);
  };

Something is transforming the arguments on the way to the client. This was not present in v11.