match 3 tutorial: unable to store gem position on the board. Whats wrong with the following code:

Error: NullReferenceException: Object reference not set to an instance of an object. Board.gemsSpawn (UnityEngine.Vector2Int pos, Gems gemsTospawn) (at Assets/my assets/scripts/Board.cs:45) Board.Setup () (at Assets/my assets/scripts/Board.cs:34) Board.Start () (at Assets/my assets/scripts/Board.cs:18)

code

public class Board : MonoBehaviour {

 public int width;
 public int height;
 public GameObject BgtilesPrefab;
 public Gems[] gems;
 
 public Gems[,] allGems;

 // Start is called before the first frame update
 void Start()
 {
     Setup();//***** line 18
     allGems = new Gems[width, height];
 }

private void Setup() { for(int x = 0; x < width; x++) { for(int y= 0; y < height; y++) { Vector2 pos = new Vector2(x,y); GameObject bgtiles = Instantiate(BgtilesPrefab, pos, Quaternion.identity); bgtiles.transform.parent = transform; bgtiles.name = "Tile NO-" + x + "," + y;

             int gemTouse = Random.Range(0, gems.Length);
             gemsSpawn(new Vector2Int(x, y), gems[gemTouse]);//*****line43
         }
     }
 }
 

private void gemsSpawn(Vector2Int pos, Gems gemsTospawn) {

     Gems gem = Instantiate(gemsTospawn, new Vector3(pos.x,pos.y,0f), Quaternion.identity);
     gem.transform.parent = transform;
     gem.name = "Gem-" + pos.x + "," + pos.y;
     allGems[pos.x, pos.y] = gem;//******line 45 
     gem.setupgems(pos,this);

 }

}