I'm getting a NullReferenceException on Camera.main

The camera in question is using the MainCamera tag, but when I try to use Camera.main, I get a null reference exception and I can't figure out why. Could someone enlighten me?

 using UnityEngine;
 using UnityEngine.UI;
 using System.Collections;
 
 public class LootPickup : MonoBehaviour {
     
     public GameObject ak47;
     public GameObject m4a1;
     public Transform gunPoint;
     //public GameObject crosshairUIobj;
     Camera myCamera;
 
     //Text lootText;
     GameObject Player;
     // Weapons:
     // 0 = Unarmed
     // 1 = m4a1
     // 2 = ak47
     int newWeapon = 0;
     
     // Use this for initialization
     void Start () {
         Player = GameObject.Find ("Player Controller(Clone)");

         //lootText = crosshairUIobj.GetComponent<Text> ();
     }
     
     // Update is called once per frame
     void Update () {
         Ray ray = new Ray(Camera.main.transform.position, Camera.main.transform.forward);
         Transform hitTransform;
         Vector3 hitPoint;
         
         hitTransform = FindClosestHitObject(ray, out hitPoint);
         
         //Debug.Log (hitTransform.gameObject.tag);
             if(hitTransform.transform.CompareTag ("ak47")){
                 newWeapon = 2;
             //lootText.text = "Pick up AK-47";
             }
             if(hitTransform.transform.CompareTag ("m4a1")){
                 newWeapon = 1;
             //lootText.text = "Pick up M4A1";
             }
         if(Input.GetKeyDown("f"))
         {
             exchangeWeapon (newWeapon);
         }
     }
 
     void exchangeWeapon(int newWeapon){
 
         if (newWeapon == 1) {
             ak47.gameObject.SetActive(false);
             m4a1.gameObject.SetActive(true);
         }
         if (newWeapon == 2) {
             ak47.gameObject.SetActive(true);
             m4a1.gameObject.SetActive(false);
         }
         if (newWeapon == 0) {
             ak47.gameObject.SetActive(false);
             m4a1.gameObject.SetActive(false);
         }
     }
 
     Transform FindClosestHitObject(Ray ray, out Vector3 hitPoint) {
         
         RaycastHit[] hits = Physics.RaycastAll(ray);
         
         Transform closestHit = null;
         float distance = 0;
         hitPoint = Vector3.zero;
         
         foreach(RaycastHit hit in hits) {
             if(hit.transform != this.transform && ( closestHit==null || hit.distance < distance ) ) {
                 // We have hit something that is:
                 // a) not us
                 // b) the first thing we hit (that is not us)
                 // c) or, if not b, is at least closer than the previous closest thing
                 
                 closestHit = hit.transform;
                 distance = hit.distance;
                 hitPoint = hit.point;
             }
         }
         
         // closestHit is now either still null (i.e. we hit nothing) OR it contains the closest thing that is a valid thing to hit
         
         return closestHit;
         
     }
 }

This is the console window output:

 NullReferenceException: Object reference not set to an instance of an object
 LootPickup.Update () (at Assets/LootPickup.cs:32)