IF Statement

SOLVED

I'm trying to create a IF statement. what I want is that if the delivery address box is not populated I want it to take the Invoice address. I have managed that BUT if not all lines are populated on the delivery address it takes it from the invoice address.... so it can sometimes have a mixture of delivery address and invoice address. 

I want my statement to be IF no delivery address/ then Invoice address but if noting populated on delivery line to leave blank. my current statement is 

SALES_ORDER.DEL_ADDRESS_1= "" ? SALES_ORDER.ADDRESS_1:SALES_ORDER.DEL_ADDRESS_1