我的应用使用ALAssetsLibrary从用户的设备获取所有照片并将其上传到我们的云服务器。我注意到用户不时会在[ALAssetRepresentation元数据]中崩溃（请参阅下面的崩溃日志）。我的设备上的任何照片都无法解决同样的问题。这是系统照片库的问题吗？我怎样才能防止这种崩溃？
谢谢
Date/Time: 2014-08-16 10:15:39.865 +0300
OS Version: iOS 7.1.1 (11D201)
Report Version: 104
Exception Type: EXC_BAD_ACCESS (SIGSEGV)
Exception Subtype: KERN_INVALID_ADDRESS at 0x00000000
Triggered by Thread: 9
....
Thread 9 Crashed:
0 CoreFoundation 0x2eeda5c2 CFDataGetBytePtr + 6
1 PhotoLibraryServices 0x358d7128 __46-[PLManagedAsset adjustmentsXMPRepresentation]_block_invoke + 224
2 CoreData 0x2ed839ca developerSubmittedBlockToNSManagedObjectContextPerform + 86
3 CoreData 0x2ed83b0e -[NSManagedObjectContext performBlockAndWait:] + 110
4 PhotoLibraryServices 0x358d6fda -[PLManagedAsset adjustmentsXMPRepresentation] + 222
5 AssetsLibrary 0x2e6f9498 __33-[ALAssetRepresentation metadata]_block_invoke + 20
6 AssetsLibrary 0x2e700862 __53-[ALAssetRepresentationPrivate _performBlockAndWait:]_block_invoke + 66
7 CoreData 0x2ed839ca developerSubmittedBlockToNSManagedObjectContextPerform + 86
8 libdispatch.dylib 0x39c2bd3c _dispatch_client_callout + 20
9 libdispatch.dylib 0x39c306be _dispatch_barrier_sync_f_invoke + 22
10 CoreData 0x2ed83b06 -[NSManagedObjectContext performBlockAndWait:] + 102
11 AssetsLibrary 0x2e6fc36a -[ALAssetsLibrary _performBlockAndWait:] + 130
12 AssetsLibrary 0x2e700624 -[ALAssetRepresentationPrivate _performBlockAndWait:] + 172
13 AssetsLibrary 0x2e6f93ec -[ALAssetRepresentation metadata] + 460
....
17 AssetsLibrary 0x2e6fe70c __56-[ALAssetsLibrary assetForURL:resultBlock:failureBlock:]_block_invoke_2 + 248
18 libdispatch.dylib 0x39c2bd50 _dispatch_call_block_and_release + 8
19 libdispatch.dylib 0x39c31684 _dispatch_root_queue_drain + 224
20 libdispatch.dylib 0x39c318d8 _dispatch_worker_thread2 + 52
21 libsystem_pthread.dylib 0x39d5cc14 _pthread_wqthread + 296
22 libsystem_pthread.dylib 0x39d5cad8 start_wqthread + 4