ActionScript :: Recommended Initialization Values For Numbers

Assume you have a variety of number or int based variables that you want to be initialized to some default value. But using 0 could be problematic because 0 is meaningful and could have side affects. I have been working in Actionscript lately and have a variety of value objects with optional parameters so for most variables I set null but for numbers or ints I can't use null. An example:

package com.website.app.model.vo {
public class MyValueObject {
public function MyValueObject (
_id:String=null,
_amount:Number=0,
[Code] .....

The difficulty is that using 0 in the above code might be problematic if the value is not ever changed from its initial value. It is easy to detect if a variable has a null value. But detecting 0 may not be so easy because 0 might be a legitimate value. I want to set a default value to make the parameter optional but I also want to later detect in my code if the value was changed from its default without hard to debug side affects. I suppose I could use something like -1 for a value. I suppose it depends on the nature of the variable and the data.