Late initialization error, but non nulling wont solve

Question

I am receiving the following error when running a build,

Another exception was thrown: LateInitializationError: Field '_pageManager@638124189' has not been initialized. Performing hot reload...

I am following this tutorial, https://suragch.medium.com/steaming-audio-in-flutter-with-just-audio-7435fcf672bf, but I want this logic in a widget that isnt main, which I think is where my confusion is coming from.

Here is a scrollbar widget, nested in a music page widget, nested in a widget initialized in main.

here is the page manager

If i change over
late final PageManager _pageManager; to PageManager? _pageManager

As i've seen in some suggestions, I receive lots of errors like this " Error: Property 'buttonNotifier' cannot be accessed on 'PageManager?' because it is potentially null." however the post calls for null safety, anyway.