I have a current formula that I need to nest with another IF formula....
=IFERROR(VLOOKUP(B15,D40:E42,2,FALSE),"Invalid Shipping option")

D40:E42 are shipping options with cost amounts that are input into cell c17

The iferror formula works, but I need to add a formula that when B15 is
blank then it will return a blank in cell C17