nullreferenceexception object reference not set to an instance of an object

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

// Use this for initialization
void Start ()
{

if(playerSpawn != null)
{
    transform.position = playerSpawn.position;  
    Debug.Log(playerSpawn);
}

}

// Update is called once per frame

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;

}

}
}

im getting this error in unity nullreferenceexception object reference not set to an instance of an object unity . im newbie. thank you for the help.

currentTrackPosition need to be initialized (with new keyword), as playerSpawn might always be null.

void OnTriggerEnter2D(Collider2D other)
{
if(other != null && other.tag != null)
{
if(other.tag == “DeadZone”)
{

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

i found the solution thank you!