Null Reference Exception on C# script

please repost your code and format it properly.

 using UnityEngine;
 using System.Collections;
 
 public class SwitchWithPickup : $$anonymous$$onoBehaviour {
 
     public string childThatWillBeReplaced;
     GameObject weapon;
     GameObject pickupTrigger;
     GameObject player;
 
 
     void Start () {
         weapon = GameObject.Find (childThatWillBeReplaced);
         player = this.gameObject;
     }
 
     void OnTriggerEnter(Collider other) {
         pickupTrigger = other.gameObject;
 
         if (other.CompareTag("pickup"))
         {
             other.tag="Weapon";
 
             Destroy(weapon);
 
             GameObject NewWeapon = Instantiate(other, transform.position, Quaternion.identity) as GameObject;
 
             NewWeapon.transform.SetParent(player.transform);
 
             Destroy(other.transform.gameObject);
 
         }
     }
 }