Cannot Read Property 'appendChild' Of Null. Javascript

I'm following a tutorial online on how to make a to do list. found here https://www.youtube.com/watch?v=MURDw0-BiEE I've following it perfectly, but it won't work. Browser states

Solution 1:

You wrote addNewItem and invoked it in a manner which expects that it should take a parameter named list but you never added it as a param in the function definition. This should straighten you up:

function addNewItem(list) {

as opposed to your

function addNewItem() {