"ArgumentNullException: Value cannot be null" for AudioSource.PlayOneShot

Question

I am working on a game and I am trying to add a sound effect.

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

public class PlayerController : MonoBehaviour
{
    private Rigidbody playerbody;
    private Animator playerAnim;
    private bool grounded;
    public bool gameover;
    public float jumpforce;
    public float gravmod;
    public ParticleSystem explosion;
    public ParticleSystem dirt;
    public AudioClip jumpSound;
    public AudioClip crashSound;
    private AudioSource playerAudio;

    // Start is called before the first frame update
    void Start()
    {
        playerbody = GetComponent<Rigidbody>();
        playerAnim = GetComponent<Animator>();
        playerAudio = GetComponent<AudioSource>();
        Physics.gravity *= gravmod;
    }

    // Update is called once per frame
    void Update()
    {
        if (Input.GetKeyDown(KeyCode.Space) && grounded && gameover == false)
        {
            playerAudio.PlayOneShot(jumpSound, 1.0f);
            playerbody.AddForce(Vector3.up * jumpforce, ForceMode.Impulse);
            playerAnim.SetTrigger("Jump_trig");
            grounded = false;
            dirt.Stop();
        }
    }
    private void OnCollisionEnter(Collision collision)
    {
        if (collision.gameObject.CompareTag("Ground"))
        {
            grounded = true;
            dirt.Play();
        }
        if (collision.gameObject.CompareTag("Obstacle"))
        {
            playerAudio.PlayOneShot(crashSound, 1.0f);
            gameover = true;
            playerAnim.SetBool("Death_b", true);
            playerAnim.SetInteger("DeathType_int", 1);
            explosion.Play();
            dirt.Stop();
        }
    }
}

At playerAudio.PlayOneShot, it just won't play and the rest of that part of the code stops working. It returns ArgumentNullException: Value cannot be null even though jumpSound and crashSound are both clearly defined. What is wrong?

Answer 1

Change your code like this:

void Start()
{
    playerbody = GetComponent<Rigidbody>();
    playerAnim = GetComponent<Animator>();
    playerAudio = GetComponent<AudioSource>();
    Physics.gravity *= gravmod;

    //log error messages indicating which GameObject is missing a reference value
    if (playerAudio == null) {
        Debug.LogError($"{nameof(playerAudio)} is null on {gameObject.name}", this);
    }
    if (playerAnim == null) {
        Debug.LogError($"{nameof(playerAnim)} is null on {gameObject.name}", this);
    }
    if (crashSound == null) {
        Debug.LogError($"{nameof(crashSound)} is null on " + gameObject.name, this);
    }
}

This will log error messages if references are missing. Logging like this should usually be the first thing you try when code isn't working like it should.

You can also use Assert.IsNotNull(), e.g.:

Assert.IsNotNull(crashSound, $"{nameof(crashSound)} is null on {gameObject.name}");

Answer 2

I got the same error while doing the guided practice project from Unity Learn.

I have fixed it by adding an Audio Source component in the Play:

1. Select the Play gameObject in the Hierarchy
2. Click the Add Component button in the Inspector and select "audioSource"

Hope my answer could help other Unity learners.

Answer 3

If your sound effects are defined but the code still won't run, its possible that the game object the script is attached to has no audio source component. You can add that under the inspector manually by selecting the object in hierarchy and adding said component, as Bing said.

Here's a short tutorial clip if it helps you: https://www.youtube.com/shorts/WbuQNmbwecc

Alternatively, you could try checking if the game object has an audio source to begin with and, if it does not have an audio source, add one in script.

You could try this:

    public class PlayerController : MonoBehaviour
    {
       // Insert all your other variables above this
       public AudioClip jumpSound;
       public AudioClip crashSound;
       private AudioSource playerAudio;

       // Start is called before the first frame update
       void Start()
       {
           // This is a bool that checks if the game object has an AudioSource or not. 
           // It returns false if there is no AudioSource, and vice versa

           if(!TryGetComponent<AudioSource>(out AudioSource source)) 
           {
              gameObject.AddComponent<AudioSource>(); // 
           }
           
           // Afterwards, we can get our AudioSource the usual way
           playerAudio = GetComponent<AudioSource>(); 
       }
    }
```