adjacent tiles within range

I made a script that highlights all tiles within a range.
It works fine when it is far from the edges but it gives me " NullReferenceException: Object reference not set to the instance of an object" at line 83

Here is the script:

public List<Tile> highlihtedTiles = new List<Tile>();
 public void HighlightAdjacentTiles(int xPos,int yPos,int _range)
    {
        int range = _range + 1;
        for (int x = -range; x < range; x++)
        {
            for (int y = -range; y < range; y++)
            {
                if (xPos - x > 0 && yPos - y > 0 && xPos + x < mapSizeX && yPos + y < mapSizeY)
                {
                    if ((Mathf.Abs(x - y) < range) && (Mathf.Abs(y + x) < range))
                    {
                        var result = tiles[xPos + x, yPos + y];
                            highlihtedTiles.Add(result);
                    }
                }
            }
        }
        for (int x = 0; x < highlihtedTiles.Count; x++)
        {
            highlihtedTiles[x].GetComponent<SpriteRenderer>().color = Color.green;// line 83
            highlihtedTiles[x].highlightd = true;
        }
    }

Seems like some of the highlightedTiles do not have a SpriteRenderer. I guess the simplest fix would be to check for any nulls:

for (int x = 0; x < highlihtedTiles.Count; x++)
{
    if (highlihtedTiles[x] != null && highlihtedTiles[x].GetComponent<SpriteRenderer>() != null)
    {
        highlihtedTiles[x].GetComponent<SpriteRenderer>().color = Color.green;// line 83
        highlihtedTiles[x].highlightd = true;
    }
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