public UnityEngine.Camera Camera;
    
    public GameObject Home01;
    public GameObject Home01Ghost;
    public GameObject ghost;
    public LayerMask raycastLayers = 1;
    public static int Placing = 0;
    public static int Home = 1;
    private RaycastHit hit;

private void Update()
    {
  if ((Placing == 1) & (Home == 1)) // Placing - переменная, обозначающая - строю я или нет. Home - ID устанавливаемого объекта.
  {
   if (ghost == null) ghost = Instantiate(Home01Ghost) as GameObject;
   else
   {
   Ray ray = Camera.ScreenPointToRay(Input.mousePosition);
    if (Physics.Raycast(ray, out hit, Mathf.Infinity, raycastLayers))
    {
     Quaternion normana = Quaternion.FromToRotation(Vector3.up, hit.normal);
     ghost.transform.position = hit.point;
     ghost.transform.rotation = normana;
     if (Input.GetMouseButtonDown(0))
     {
      GameObject Roo = Instantiate(Home01, ghost.transform.position, ghost.transform.rotation) as GameObject;
     Placing = 0;
      Destroy(ghost);
      
     }
    }
   }

  }
  }

Ray ray = Camera.ScreenPointToRay(Input.mousePosition);

Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition);

NullReferenceException: Object reference not set to an instance of an object
GUIz.Update () (at Assets/Script/Interface/GUIz.cs:127)