I was doing this:

@line_items = LineItems.find_all_by_invoice_id(params[:id])

@payments = Payments.find_all_by_invoice_id(params[:id])

@total = @line_items.sum{ |item| item.cost }

@payment_total = @payments.sum{ |payment| payment.value }

@balance = @total - @payment_total

But when no payments had been made it was coming up with an error when

trying to sum nil, so I did this:

begin

@payment_total = @payments.sum{ |payment| payment.value }

rescue

@payment_total = 0

end

So, when the sum failed it returned @payment_total as zero. Now, SURELY,

there's a better way to do this? I'm sure it's obvious when you know

how. Please, enlighten me.