Why i am getting the NullReference Error on my transform.position?

Question

I am makin a script from moving the camera and i get this error : NullReferenceException: Object reference not set to an instance of an object

but my script works, no crash or something just this error on the console, do you know why ? there is the code :

  public Transform target;
  public Transform[] views;
  public Camera cam;

  public float lerpSpeed;
  Transform currentView;


    // Update is called once per frame
    void Update()
    {
        if (Input.GetKeyDown(KeyCode.Alpha1)){
            currentView = views[0];
        }
        if (Input.GetKeyDown(KeyCode.Alpha2)){
            currentView = views[2];
        }
        if (Input.GetKeyDown(KeyCode.Alpha3)){
            currentView = views[1];
        }
        if (Input.GetKeyDown(KeyCode.Alpha4)){
           currentView = views[3];
        }


    }

    void LateUpdate() {
        cam.transform.position = Vector3.Lerp(cam.transform.position,currentView.position, lerpSpeed * Time.deltaTime);
        cam.transform.LookAt(target);
    }