Override indexOf() for call from null

I know that it is possible to override Functions in JS like this:

var indexOf = String.prototype.indexOf;
String.prototype.indexOf = function(){
    return indexOf.call(this, arguments);

This is overriding indexOf() called from a String.
Is it possible to Override indexOf() which will be called from null?
var a = null; a.indexOf("foo") should return -1. Evil right?

Source: stackoverflow-javascript