Express-Validator .optional is not passed to every field - node.js

Question

I'm playing around with express-validator attempting to apply the .optional method to my request body, but it does not act as I would expect.
I split my sanitization and validation into two files as such:
//common/middlewares/input.sanitization.middleware.js
const { body } = require('express-validator');
exports.patchSanitizationRules = () => {
return [
body('*')
.escape(),
body(['first_name', 'last_name'])
.trim()
.optional(),
body('email')
.trim()
.normalizeEmail()
.optional()
];
};
//common/middlewares/input.validation.middleware.js
const { body, validationResult } = require('express-validator');
exports.validate = (request, response, next) => {
const errors = validationResult(request);
if (!errors.isEmpty()) {
return response.status(422).send({errors: errors});
}
// Checking everything was passed correctly
console.log(request.body);
return next();
};
exports.patchValidationRules = () => {
return [
body()
.notEmpty()
.isLength({min: 4, max: 64}),
body(['first_name', 'last_name'])
.isAlpha()
.optional(),
body('email')
.isEmail()
.optional()
];
};
//users/routes.config.js
const UserController = require('./controllers/users.controller');
const UserSanitizationMiddleware = require('../common/middlewares/input.sanitization.middleware')
const UserValidationMiddleware = require('../common/middlewares/input.validation.middleware');
exports.routesConfig = (app) => {
app.patch('/users/:userId', [
UserSanitizationMiddleware.patchSanitizationRules(),
UserValidationMiddleware.patchValidationRules(),
UserValidationMiddleware.validate,
UserController.patchById
]);
};
So you may already see my issue here. I would like to place .optional into my body() or body('*'). However, doing this will cause whatever field was not in my body to be replaced by "". Now I could add logic in my controller to not allow "" as a valid value, but I would prefer to handle this within my middleware. How can I edit this?