How to keep keys for optional fields in matchedData?

[stenneepro]

Describe the bug

I want to keep keys for optional fields in request body in matchedData return value.

To Reproduce

Let's say we have user model.

interface User {
  firstName?: string;
  lastName?: string;
  email: string
}

In frontend, user removed first name. and other fields are not changed.
So frontend sends request with only changed fields.

{"firstName": null}

In this case matchedData function returns empty JSON, but I would like to keep firstName key.
There is a parameter called includeOptional, but if we set that parameter to True, matchedData function returns JSON which contains both firstName and lastName as key.

{
  "firstName": null,
  "lastName": null
}

Moreover, I think it's more accurate that if keys exist in both request and validation schema, it should exist in matchedData return value.

Environment:

• Express-validator version: 7.0.1
• Express version: 4.18.2
• Node.js version: 20.11.0