Implementation of Array.prototype.toLocaleString

I’m interested in the following piece of code written in JS:

const array = [1,2,3];
const locales = 'en-US';
const options = null;
console.log(array.toLocaleString(locales,options));

Before Node.js 20, this would output 1,2,3. However, in Node.js 20, it now throws the following error:

Uncaught TypeError: Number.prototype.toLocaleString called on null or undefined
    at Number.toLocaleString (<anonymous>)
    at Array.toLocaleString (<anonymous>)

I’m trying to understand what changed in the implementation. Specifically, I’m looking for the exact line of code that was changed in the source code. I reviewed the ECMAScript language specification but couldn’t find any related changes. My focus is on identifying where the code changed in the implementation, rather than understanding the reasoning behind it. Please point me to the right direction.

The reason for this question is because I have a library that introduced a new data structure and provides similar methods as array. I want my DS and the array to have same results for any kind of input, including for null. Once I noticed that between versions, toLocaleString provides a different result, I understood that I need to update my own toLocaleString to support the latest changes. In order to do so, I’m trying to find out the exact change in order to see in my own eyes the change.