这是我的播放器spawn的代码，但我得到了一个空引用异常错误。

public class PlayerSpawn : MonoBehaviour 
{
    public Transform playerSpawn;
    public Vector2 currentTrackPosition;
    public bool activeRespawnTimer = false;
    public float respawnTimer = 1.0f;
    public float resetRespawnTimer = 1.0f;

    void Start () 
    {       
        if(playerSpawn != null)
        {
            transform.position = playerSpawn.position;  
            Debug.Log(playerSpawn);
        }
    }
    
    void Update () 
    {
        if(activeRespawnTimer)
        {
            respawnTimer -= Time.deltaTime;
        }
        
        if(respawnTimer <= 0.0f)
        {
            transform.position = currentTrackPosition;
            respawnTimer = resetRespawnTimer;
            activeRespawnTimer = false;
        }
    }
    
    void OnTriggerEnter2D(Collider2D other)
    {
        //im getting the error messege at this position
        if(other.tag == "DeadZone")
        {
            activeRespawnTimer = true;  
        }

        if(other.tag == "CheckPoint")
        {
            currentTrackPosition = transform.position;
        }
    }
}

有什么问题吗？谢谢你的帮助。