NullReferenceException: Object reference not set to an instance of an object

Hello every. I have finished all my coding stuff and i was designing my levels. i have designed the first level(scene) without any error or something .As I moved to design second scene , I got some problem saying"NullReferenceException: Object reference not set to an instance of an object". As I have the used the same prefabs on both level, but instead of that it shows the error. It's like that when a player hit a object it dies and re spawn after 2s. This works perfectly in first scene but encountered a error in second scene. Here are parts of the code that i have used.

|||||||||||||||||||||||||||||||||| //InstaKill class attached to the object responsible for player to die

 using UnityEngine;
 using System.Collections;
 
 public class InstaKill : MonoBehaviour 
 {
 
     public void OnTriggerEnter2D(Collider2D coll)
     {
         if (coll.gameObject.tag == "Player") 
         {
             print (" you are in insta kill class");
 
             if(coll.gameObject!=null)
             LevelManager.Instance.KillPlayer (); //error that I have encountered
         }
     }
 }

|||||||||||||||||||||||||||||||||||||||||| LevelManager class

 public class LevelManager : MonoBehaviour {
 
     public static LevelManager Instance {get; private set;}
           public PlayerControl playerctrl{ get; private set; }
 
 public void Awake()
     {Instance = this;}
 
 public void KillPlayer()
     {StartCoroutine (KillPlayercode ());}
 
     private IEnumerator KillPlayercode()
     {
         playerctrl.Kill ();
         cameractrl.IsFollowing = false;
         yield return new WaitForSeconds (2f);
         cameractrl.IsFollowing = true;
         print ("KillPlayer code is going to Respawn");
         if (_CurrentCheckPointIndex != -1)
             _CheckPoints [_CurrentCheckPointIndex-1].SwapnPlayer (playerctrl);
         //TODO : Keys
     }
 }

||||||||||||||| PlayerControler attached to Player

   public class PlayerControl : MonoBehaviour
     {
     public void RespanwnAt(Transform spawnPoint)
         {
             if (!facingRight)
                 Flip ();
             IsDead = false;
     
             ThePlayerBoxColl.enabled = true;
             transform.position = spawnPoint.position;
         }
     }
 

|||||||||||||||||||||||||||||||| error I am getting when player comes in contact with other object that is responsiple for player to die NullReferenceException: Object reference not set to an instance of an object InstaKill.OnTriggerEnter2D (UnityEngine.Collider2D coll) (at Assets/_Scripts/InstaKill.cs:14)