Todos os áudios funcionam menos o da morte do Zumbi

ERRO:

PlayOneShot was called with a null AudioClip.
UnityEngine.AudioSource:PlayOneShot(AudioClip)
Bala:OnTriggerEnter(Collider) (at Assets/Scripts/Bala.cs:28)

Script audio:

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

public class ControlaAudio : MonoBehaviour
{
  private AudioSource meuAudioSource;
  public static AudioSource instancia;

  void Awake ()
  {
      meuAudioSource = GetComponent<AudioSource>();
      instancia = meuAudioSource;
  }
}

Script BALA:

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

public class Bala : MonoBehaviour {

    public float Velocidade = 20;
    private Rigidbody rigidbodyBala;
    public AudioClip MorteZumbi;

    private void Start()
    {
        rigidbodyBala = GetComponent<Rigidbody>();
    }

    // Update is called once per frame
    void FixedUpdate () {
        rigidbodyBala.MovePosition
            (rigidbodyBala.position + 
            transform.forward * Velocidade * Time.deltaTime);
    }

    void OnTriggerEnter(Collider objetoDeColisao)
    {
        if(objetoDeColisao.tag == "Inimigo")
        {
            Destroy(objetoDeColisao.gameObject);
            ControlaAudio.instancia.PlayOneShot(MorteZumbi);
        }

        Destroy(gameObject);
    }
}