How do I use a switch with a null variable?

Question

Here is my current situation...
I have a form that will take the inputted information in the field "LEDIR" and divide it by the information in field "AMMO".  I get errors when the form is first loaded because the field "AMMO" is blank and causes a "Divide by 0" problem.   I tried to solve the problem with a switch, but an not sure how to create a "null" switch case.  Here is what I have.. any ideas as to how I can set the second case so it returns a "0" for a null AMMO field?
var InvR = this.getField("LEDIR").valueAsString;
var AmmoPk = this.getField("AMMO").valueAsString;
switch (Ammo)
case "0":
   event.value = 0;
   break;
case "[what do i put here?] ":
   event.value = 0;
   break;
default:
   event.value = (Math.floor(InvR/AmmoPk))
any ideas as to how I can set the second case so it returns a "0" when the AMMO field is empty?

Answer 1

You can even stack the 'case' to create and 'OR' type of selection:
var InvR = this.getField("LEDIR").valueAsString;
var AmmoPk = this.getField("AMMO").valueAsString;
switch (Ammo) {
case "0":
case "":
   event.value = 0;
   break;
default:
   event.value = (Math.floor(InvR/AmmoPk))
But it is just as easy to use:
var InvR = Number(this.getField("LEDIR").value);
var AmmoPk = Number(this.getField("AMMO").value);
event.value = "";
if(AmmoPk != 0) {
  event.value = (Math.floor(InvR/AmmoPk))