public Dictionary <int?, DatabaseModel.Vendor> GetActiveVendors(Dictionary <int?, Customer> allActiveCustomers, VendorService vendorService, RecurringInvoices.Frequency paymentFrequency)
{
var activeVendors = vendorService.GetByPaymentFrequency(paymentFrequency)
.Where(x => allActiveCustomers.ContainsKey(x.QuickBooksOnlineId))
.ToDictionary(x => x.QuickBooksOnlineId);
return(activeVendors);
}