❔ Object reference set to null

var showTime = ShowTimes.Where(x => x.ShowTimeID == request.ShowTimeId).FirstOrDefault();

    int totalTicketsRequested = request.RequireTickets.Count();

    if (showTime.Theatre.SeatingSize < totalTicketsRequested)
    {
        throw new Exception("There are not enough seats available for this purchase");
    }

var showTime = ShowTimes.Where(x => x.ShowTimeID == request.ShowTimeId).FirstOrDefault();

    int totalTicketsRequested = request.RequireTickets.Count();

    if (showTime.Theatre.SeatingSize < totalTicketsRequested)
    {
        throw new Exception("There are not enough seats available for this purchase");
    }