Setup To Get Form Field Filled Automatically

Basically, I've setup a form to have all the required data written to a csv file. Now, The only thing is some of the non-required fields are filled in and some people don't fill them in, so when I import it into excel, the fields move about. What I need to know, is there a condition I can set to have a value written into all the empty fields when it is submitted?

Here is where I am with that so far:
if (app100.address2.value == "") {
doc.write("N/A");
}