Opening a door outwards from the player whenever a player is colliding it.c#

I tried looking around and cant seem to find any door related to be similar to what I am looking for. Would like to ask for assistance on this.

 using UnityEngine;
 using System.Collections;
 
 public class newdooropen : MonoBehaviour
 {
     Animator anim;
     bool doorOpen = false;
   
     bool playerstillhere = false;
   void Start() {
        anim= GetComponent<Animator>();
 
     }
     void Update()
     {
         
 
     }
     void OnTriggerEnter(Collider other)
     {
         if (other.tag == "Player") {
          
             if (playerstillhere==false)
             {
                 if (doorOpen==false)
                 {
 
                     doorOpen = true;
                    
                 }
                 else
                 {
                     
                     doorOpen = false;
                    
                 }
                 playerstillhere = true;
                
             }
 
 
         }
         anim.SetBool("PlayerIsThere", playerstillhere);
         anim.SetBool("DoorStatus", doorOpen);
 
     }
     void OnTriggerExit(Collider another)
     {
         if (another.tag == "Player")
         {
 
             
             playerstillhere = false;
             anim.SetBool("PlayerIsThere", playerstillhere);
         }
 
     }
 }
 

This keeps giving me an error. NullReferenceException: Object reference not set to an instance of an object newdooropen.OnTriggerEnter (UnityEngine.Collider other) (at Assets/newdooropen.cs:43)