Property does not exist on type 'string'.ts(2339)

So here is my code and I have this error and I don't understand why. I need some help here... I don't know why is this happening : Property does not exist on type 'string'.ts(2339) at :return users.find(u => u.userName === user.userName && u.password === user.password) on u.userName and u.password . PLease help .

import { Injectable } from '@angular/core';

@Injectable({
providedIn: 'root'
})
export class AuthService {

constructor() { }

authUser(user: any) {
let users : string[] = [];
if(localStorage.getItem('Users')) {
users = JSON.parse(localStorage.getItem('Users') || '{}');
}
return users.find(u => u.userName === user.userName && u.password === user.password)
}
}

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