Disconnecting from chromecast while video is playing produces an uncaught runtime error

[HazardousPeach]

This issue respects the following points:

• This issue is not already reported on GitHub (I've searched it).
• I agree to follow Jellyfin's Code of Conduct.
• This report addresses only a single issue; If you encounter multiple issues, kindly create separate reports for each one.

Describe the bug

Basically what it says in the title. In the current master branch of jellyfin-web, disconnecting from a cast while a video is playing produces a big backtrace about player being null.

Reproduction Steps

1. Clone the repository
2. npm install && npm start
3. Click the cast icon in the upper right and select a google chromecast device
4. Start playing a video
5. While the video is playing, click the cast icon in the upper right and click "disconnect"
6. Error appears

Expected/Actual behaviour

I expect the app to disconnect from the chromecast without error, returning to a non-casting state where it is free to cast to other chromecasts. Instead, it produces a big runtime error backtrace across the entire app with three copies of the backtrace.

Logs

ERROR
player cannot be null
at PlaybackManager.self.getPlayerState (webpack-internal:///./components/playback/playbackmanager.js:2125:15)
at MediaSessionSubscriber.onMediaSessionUpdate (webpack-internal:///./apps/stable/features/playback/utils/mediaSessionSubscriber.ts:148:62)
at MediaSessionSubscriber.onPlayerChange (webpack-internal:///./apps/stable/features/playback/utils/mediaSessionSubscriber.ts:197:14)
at eval (webpack-internal:///./utils/events.ts:59:22)
at Array.forEach ()
at Object.trigger (webpack-internal:///./utils/events.ts:58:14)
at triggerPlayerChange (webpack-internal:///./components/playback/playbackmanager.js:244:61)
at setCurrentPlayerInternal (webpack-internal:///./components/playback/playbackmanager.js:1013:7)
at PlaybackManager.self.setActivePlayer (webpack-internal:///./components/playback/playbackmanager.js:876:9)
at PlaybackManager.setDefaultPlayerActive (webpack-internal:///./components/playback/playbackmanager.js:3981:12)

Server version

10.11.6-1

Web version

a30dd7e

Build version

a30dd7e

Platform

Linux

Browser

Chrome Version 144.0.7559.132 (Official Build) (64-bit)

Additional information

No response

[HazardousPeach]

From what I can tell, this comes from a few different parts of the code disagreeing on what the representation of a "local" player should be. To PlaybackManager.setActivePlayer, a local player should be represented as null, since there is no remote player:

if (player === 'localplayer' || player.name === 'localplayer') {
    if (self._currentPlayer?.isLocalPlayer) {
        return;
    }
    setCurrentPlayerInternal(null, null);
    return;
}

This sets PlaybackManager._currentPlayer and PlaybackSubscriber.player to null eventually (the latter through an event that gets triggered). However, MediaSessionSubscriber does not appear to think that player should ever be null, because when onMediaSessionUpdate is called without a second argument (which onPlayerChange does later in the chain), it calls PlaybackManager.getPlayerState on its self.player. I think that getPlayerState is only supposed to be called on remote players, because when it receives a null, and the PlaybackManager doesn't have its own non-null currentPlayer, it throws the 'player cannot be null' error.

From later logic in MediaSessionSubscriber, it seems to think that a local player should be represented as a non-null object with an isLocalPlayer attribute set to true. But I don't think that can actually happen; the only place I see isLocalPlayer set to non-false in the codebase is in a branch when its already non-false (turning a non-false value thats not true into a real true).

EDIT: Oh isLocalPlayer is actually true by default on anything that doesn't set it explicitly to false like the remote players.