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

Questions & Answers
1

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);

}

}

2

@MelvMay