why is unity set tile not working?

Hi, umm I have a small problem where I auto-generate a tilemap. However, when tiles are re-saved and unloaded on a chunk, it saves incorrectly. To be more clear, I am using a Tilebase grid like this TileBase[,] baseGrid; and I resave and THEN set the tile to null, but it puts the save too null as well. //first - all tiles are set to random red tile baseGrid[x, y] = baseTilemap.GetTile(new Vector3Int(x + chunkOffset.x, y + chunkOffset.y, 0)); //second - set all tiles to all but not the save baseTilemap.SetTile(new Vector3Int(x + chunkOffset.x, y + chunkOffset.y, 0), null); //save becomes null Do you have any idea for why this might not be working? Thanks, Oregano