what happens ?
0 CoreFoundation 0x00000001d1b55294 + 252
1 libobjc.A.dylib 0x00000001d0d2f9f8 objc_exception_throw + 56
2 CoreData 0x00000001d4714694 + 0
3 CoreData 0x00000001d4714868 + 208
4 CoreData 0x00000001d4714af8 + 608
5 CoreData 0x00000001d45aad14 + 240
6 CoreData 0x00000001d45ab99c + 844
7 CoreData 0x00000001d45ab9c8 + 888
8 CoreData 0x00000001d45ac81c + 1592
9 XMPPFramework 0x00000001056d7920 -[XMPPCoreDataStorage save] + 304
10 XMPPFramework 0x00000001056d7e98 __37-[XMPPCoreDataStorage scheduleBlock:]_block_invoke + 76
11 libdispatch.dylib 0x00000001d1594a38 + 24
12 libdispatch.dylib 0x00000001d15957d4 + 16
13 libdispatch.dylib 0x00000001d1570dec + 548
14 libdispatch.dylib 0x00000001d157192c + 408
15 libdispatch.dylib 0x00000001d1579e08 + 584
16 libsystem_pthread.dylib 0x00000001d1775114 _pthread_wqthread + 304
17 libsystem_pthread.dylib 0x00000001d1777cd4 start_wqthread + 4