Why is my destroy platform script now working? NullReferenceException: Object reference not set to an instance of an object.

 using UnityEngine;
 using System.Collections;
 
 public class PlatformDestroyer : MonoBehaviour {
 
     public GameObject platformDestructionPoint;
 
     // Use this for initialization
     void Start () {
         platformDestructionPoint = GameObject.Find ("PlatformDestructionPoint");    
     }
     
     // Update is called once per frame
     void Update () {
             
         if(transform.position.x < platformDestructionPoint.transform.position.x)
         {
             Destroy (gameObject);
         }
 
     }
 }
 

Hello, I am a complete beginner to Unity and am trying to learn by following a 2d endless runner tutorial. So far it has been well, but when trying to create a script that destroys platforms after my character passes by I keep getting an error message. It has something to do with line 16 of my code and I have no idea what it means or how to fix it. Please help me to fix my problem. Thank you!