NPE when loading the duration result to Flutter

[snipd-min]

Which API doesn't behave as documented, and how does it misbehave?
In the - (void)load:(NSDictionary *)source initialPosition:(CMTime)initialPosition initialIndex:(NSNumber *)initialIndex result:(FlutterResult)result method, the _loadResult(@{@"duration": @([self getDurationMicroseconds])}); at line 693 could throw a NPE when the _loadResult is already reported via observeValueForKeyPath at line 814.

if (_indexedAudioSources.count == 0 || !_player.currentItem ||
            _player.currentItem.status == AVPlayerItemStatusReadyToPlay) {
        _processingState = ready;
        _loadResult(@{@"duration": @([self getDurationMicroseconds])});      // <--- the NPE happened here
        _loadResult = nil;
    } else {
        // We send result after the playerItem is ready in observeValueForKeyPath.
    }

I'm not sure if observeValueForKeyPath should ever report the duration before the load method, but here in theory the _loadResult could be set to nil and should probably check for it before calling.

Here I attached the crash log trace from xcode via the Organizer > Crashes:

Minimal reproduction project
Unfortunately I couldn't find a way to reproduce this after a lot of tries. I still feel like I should report it as it's quite clear what actually happened here (or should have happened). This only happens to a very small fraction of users that we have.

Error messages

Crashed: com.apple.main-thread
EXC_BAD_ACCESS KERN_INVALID_ADDRESS 0x0000000000000010

Crashed: com.apple.main-thread
0  just_audio                     0x74cc -[AudioPlayer load:initialPosition:initialIndex:result:] + 1900
1  just_audio                     0x47ec -[AudioPlayer handleMethodCall:result:] + 524
2  just_audio                     0x45a8 __70-[AudioPlayer initWithRegistrar:playerId:loadConfiguration:userAgent:]_block_invoke + 72
3  Flutter                        0x5c0a8c InternalFlutterGpu_Texture_AsImage + 6316
4  Flutter                        0x43d0c (Missing UUID 4c4c44ef55553144a1c675e6577e3daa)
5  libdispatch.dylib              0x213c _dispatch_call_block_and_release + 32
6  libdispatch.dylib              0x3dd4 _dispatch_client_callout + 20
7  libdispatch.dylib              0x125a4 _dispatch_main_queue_drain + 988
8  libdispatch.dylib              0x121b8 _dispatch_main_queue_callback_4CF + 44
9  CoreFoundation                 0x56710 __CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__ + 16
10 CoreFoundation                 0x53914 __CFRunLoopRun + 1996
11 CoreFoundation                 0x52cd8 CFRunLoopRunSpecific + 608
12 GraphicsServices               0x11a8 GSEventRunModal + 164
13 UIKitCore                      0x40aae8 -[UIApplication _run] + 888
14 UIKitCore                      0x4bed98 UIApplicationMain + 340
15 Runner                         0x97a8 main + 8 (AppDelegate.swift:8)
16 ???                            0x1c1f47154 (Missing)

Expected behavior
In case the duration is already reported via observeValueForKeyPath, the _loadResult doesn't need to be called and should just move on.

Screenshots
N/A

Smartphone (please complete the following information):

• Device: iOS
• OS: iOS 15-18

Flutter SDK version
[✓] Flutter (Channel stable, 3.24.3, on macOS 15.1.1 24B91 darwin-arm64, locale
en-US)
• Flutter version 3.24.3 on channel stable at
/Users/minzhao/fvm/versions/3.24.3
• Upstream repository https://github.com/flutter/flutter.git
• Framework revision 2663184aa7 (3 months ago), 2024-09-11 16:27:48 -0500
• Engine revision 36335019a8
• Dart version 3.5.3
• DevTools version 2.37.3

[✓] Android toolchain - develop for Android devices (Android SDK version 33.0.1)
• Android SDK at /Users/minzhao/Library/Android/sdk
• Platform android-34, build-tools 33.0.1
• ANDROID_HOME = /Users/minzhao/Library/Android/sdk
• ANDROID_SDK_ROOT = /Users/minzhao/Library/Android/sdk
• Java binary at: /Applications/Android
Studio.app/Contents/jbr/Contents/Home/bin/java
• Java version OpenJDK Runtime Environment (build
17.0.11+0-17.0.11b1207.24-11852314)
• All Android licenses accepted.

[✓] Xcode - develop for iOS and macOS (Xcode 16.1)
• Xcode at /Applications/Xcode.app/Contents/Developer
• Build 16B40
• CocoaPods version 1.15.2

[✓] Chrome - develop for the web
• Chrome at /Applications/Google Chrome.app/Contents/MacOS/Google Chrome

[✓] Android Studio (version 2024.1)
• Android Studio at /Applications/Android Studio.app/Contents
• Flutter plugin can be installed from:
🔨 https://plugins.jetbrains.com/plugin/9212-flutter
• Dart plugin can be installed from:
🔨 https://plugins.jetbrains.com/plugin/6351-dart
• Java version OpenJDK Runtime Environment (build
17.0.11+0-17.0.11b1207.24-11852314)

[✓] VS Code (version 1.95.3)
• VS Code at /Applications/Visual Studio Code.app/Contents
• Flutter extension version 3.98.0

[✓] Network resources
• All expected network resources are available.

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This issue has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs, or use StackOverflow if you need help with just_audio.