Getting A NullReferenceException trying to make a simple room trasition in my first game

Question

So im trying to make a simple room transition by having the camera basically flip into a new area after the "player" hits the collider.

here is the errors:

NullReferenceException: Object reference not set to an instance of an object RoomMove.Start () (at Assets/Scripts/RoomMove.cs:14)

NullReferenceException: Object reference not set to an instance of an object RoomMove.OnTriggerEnter2D (UnityEngine.Collider2D player) (at Assets/Scripts/RoomMove.cs:26)

here is the code:

using System.Collections.Generic;
using UnityEngine;
using UnityEngine.UI;

public class RoomMove : MonoBehaviour
{
    public Vector2 cameraChangeMax;
    public Vector2 cameraChangeMin;
    public Vector3 playerChange;
    private CameraMovement cam;
    
    // Start is called before the first frame update
    void Start()
    {
        cam = Camera.main.GetComponent<CameraMovement>();
    }

    // Update is called once per frame
    void Update()
    {

    }
    private void OnTriggerEnter2D(Collider2D player)
    {
        if (player.CompareTag("Player"))
        {
            cam.minPosition += cameraChangeMin;
            cam.maxPosition += cameraChangeMax;
            player.transform.position += playerChange;
        }
    }

}