Getting NullPointer Exception Error in Simple ArrayList program

Hi,

I am creating a simple ArrayList program that would enable one to input their username to it using a scanner. However, i am getting this error:

"Exception in thread "main" java.lang.NullPointerException

at home.Members.addUser(Members.java:16)

at home.Main.main(Main.java:14)"

Here is the code! :

Main.java class

Java Code:

import java.util.Scanner;

public class Main {

        public static void main(String[] args) {
                String username;
                Members online = new Members();
                Scanner input = new Scanner(System.in);
                
                System.out.println("Enter your username");
                username = input.nextLine();            
                online.addUser(username);
                
                

        }
}

Members.java class

Java Code:

package home;
import java.util.ArrayList;

public class Members {
        
        public ArrayList<String> users;
        
        public Members() {
                
                ArrayList<String> users = new ArrayList<>();
                
        }
        
        public void addUser(String username) {
                
                users.add(username);
                
        }       

}

Im guessing this is a really simple mistake somewhere but i cant figure it out.

Thank you!