I need a way to use my formula even when there is no discount.

I
45 Tuition $1596.00
46 Registration Fee $25.00
47 Textbook $75.00
48 Group Discount 5%
49 Total I45-(I45*I48)+I46+I47

Formula works, but what if there's no discount? If cell I48 is blank then I
get #value. I want it to total my numbers even if there is no discount.
Thanks for looking at this.

Rob