NullReferenceException when trying to join the game

[kaktusyonok]

Hello everybody,
So the hosting works fine, but the joining doesnt work. when i host from the editor (to see the join code), and try to join from the build nothing happens, so i added a join code display in the game scene, so i can host from the build to see the exception. and i get this every time i click the client button (even if the join code is correct/wrong):

here is my related code:

using System.Collections;
using System.Collections.Generic;
using TMPro;
using UnityEngine;

public class MainMenu : MonoBehaviour
{
    [SerializeField] private TMP_InputField joinCodeField;

    public async void StartHost()
    {
        await HostSingleton.Instance.GameManager.StartHostAsync();
    }

    public async void StartClient()
    {
        await ClientSingleton.Instance.GameManager.StartClientAsync(joinCodeField.text);
    }
}

using System.Collections;

using System.Collections.Generic;

using System.Threading.Tasks;

using UnityEngine;

public class ClientSingleton : MonoBehaviour

{

    private static ClientSingleton instance;

    public ClientGameManager GameManager {get; private set; }

    public static ClientSingleton Instance

    {

        get

        {

            if (instance != null) return instance;

            instance = FindObjectOfType<ClientSingleton>();

            if (instance = null)

            {

                Debug.LogError("No ClientSingelton found!!!!!!!!!!!");

                return null;

            }

            return instance;

        }

    }

    private void Start()

    {

        DontDestroyOnLoad(gameObject);

    }

    public async Task<bool> CreateClient()

    {

       GameManager = new ClientGameManager();

       return await GameManager.InitAsync();

    }

}

using System;
using System.Collections;
using System.Collections.Generic;
using System.Threading.Tasks;
using Unity.Netcode;
using Unity.Netcode.Transports.UTP;
using Unity.Networking.Transport.Relay;
using Unity.Services.Core;
using Unity.Services.Relay;
using Unity.Services.Relay.Models;
using UnityEngine;
using UnityEngine.SceneManagement;

public class ClientGameManager
{
    private JoinAllocation allocation;

    private const string MenuSceneName = "Menu";

    public async Task<bool> InitAsync()
    {
        await UnityServices.InitializeAsync();

        AuthState authState = await AuthenticationWrapper.DoAuth();

        if(authState == AuthState.Authenticated)
        {
            return true;
        }

        return false;
    }

    public void GoToMenu()
    {
        SceneManager.LoadScene(MenuSceneName);
    }

    public async Task StartClientAsync(string joinCode)
    {
        try
        {
            allocation = await Relay.Instance.JoinAllocationAsync(joinCode);
        }
        catch(Exception e)
        {
            Debug.Log(e);
            return;
        }

        UnityTransport transport = NetworkManager.Singleton.GetComponent<UnityTransport>();

        RelayServerData relayServerData = new RelayServerData(allocation, "dtls");
        transport.SetRelayServerData(relayServerData);

        NetworkManager.Singleton.StartClient();
    }
}

i tried changing dtls to udp and its not working. i copy pasted the code from the repository and its not working. What it could be?
All the references are set correctly(host, client buttons, input fields etc.)

[kaktusyonok]

Update:
after some debugging it turns out that the ClientSingleton.Instance is null.

[kaktusyonok]

Update: I solved the issue!
because the ClientSingleton.Instance is null i modified the main menu script:

using System.Collections;
using System.Collections.Generic;
using TMPro;
using UnityEngine;

public class MainMenu : MonoBehaviour
{
    [SerializeField] private TMP_InputField joinCodeField;

    public async void StartHost()
    {
        await HostSingleton.Instance.GameManager.StartHostAsync();
    }

    public async void StartClient()
    {
        if (ClientSingleton.Instance == null) ClientSingleton.SetInstance(FindObjectOfType<ClientSingleton>());
        await ClientSingleton.Instance.GameManager.StartClientAsync(joinCodeField.text);
    }
}

(SetInstance() is a function that i added in the ClientSingleton)

    public static void SetInstance(ClientSingleton clientSingleton)
    {
        instance = clientSingleton;
    }

this worked for me once, then stopped working. But changing “dtls” to “udp” fixed the issue

[Yitzchak_Cohen]

Glad you figured this out, well done!

[bixarrio]

You are manually doing exactly what the Instance property getter is supposed to do, but there’s an error in that code. You should instead fix the error. Here’s where a typo caused you headaches (it’s in ClientSingleton):

    public static ClientSingleton Instance
    {
        get
        {
            if (instance != null) return instance;
            instance = FindObjectOfType<ClientSingleton>();
            if (instance = null) // <-- Right here
            {
                Debug.LogError("No ClientSingelton found!!!!!!!!!!!");
                return null;
            }
            return instance;
        }
    }

I have marked the offending line above. You are setting instance back to null there. = is assignment, == is comparison. You just needed to add another = and everything would have been fine. It is for this exact reason why old-school C/C++ devs write if (null == instance) (putting null first) because then it wouldn’t even compile if you try to assign something to null. Your IDE (if it’s proper) should also have complained a little about it

[kaktusyonok]

Thanks, that was the issue! By the way, my IDE is visual studio code.