Object reference not set to an instance of an object

I'm trying to make a script that lets me switch from one camera to another but I keep getting the same error

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class Switch : MonoBehaviour {
 
     GameObject Camera1;
     GameObject Camera2;
 
     // Update is called once per frame
     void Update () {
         if (Input.GetKeyDown("1"))
         {
             Camera1.SetActive(true);
             Camera2.SetActive(false);
         }
         if (Input.GetKeyDown("2"))
         {
             Camera1.SetActive(false);
             Camera2.SetActive(true);
         }
     }
 }