`Cannot read properties of undefined (reading 'element')` during cleanup

Description

Occasionally, when tearing down via rive-react's useRive hook, we're seeing an error in rive-wasm / canvas:

Cannot read properties of undefined (reading 'element') (see screenshot of stack track below)

Provide a Repro

I don't have a repro, but I do have a stacktrace from our Sentry instance:

This clearly shows that observed is undefined.

Our usage is extremely simple:

function CorrectAnimation() {
  const { RiveComponent, rive } = useRive({
    src: getStaticAssetPath('anims/correct-animation.riv'),
    autoplay: true,
    layout: new Layout({ fit: Fit.Cover, alignment: Alignment.TopCenter }),
  });

  return <RiveComponent />;
}

Browser & Versions

Browser: Chrome 130, Firefox 131 (we've seen the error in both)
OS: macOS 10.15
pnpm -v: 9.5.0
@rive-app/react-canvas 4.15.2
@rive-app/canvas 2.22.0

Additional context

What I believe is happening:

There is a null check here: https://github.com/rive-app/rive-wasm/blob/9138225b8667d11fd492ff59039074b77f0c21f7/js/src/rive.ts#L2104-L2106

But not an undefined check, resulting in observed being undefined and then erroring out when observed.element is attempted to be resolved.

As to why observed is undefined, I am not sure. I see that it's conditionally initialized in the constructor... although I don't quite understand how that condition could be false.

https://github.com/rive-app/rive-wasm/blob/9138225b8667d11fd492ff59039074b77f0c21f7/js/src/rive.ts#L1564-L1569

One straightforward fix might simply be initializing it to null here (but this does not answer why):

https://github.com/rive-app/rive-wasm/blob/9138225b8667d11fd492ff59039074b77f0c21f7/js/src/rive.ts#L1491-L1492

rive-app / rive-wasm