null pointer dereference when executeFetchRequest: invoked

[fantexi023]

crash info as follows:
Exception Type: EXC_BAD_ACCESS (SIGSEGV)
Exception Codes: 0x00000000 at 0x0000000000000000
Crashed Thread: 51

Thread 51 Crashed:
0 CoreData _fetchResultSetAllocateInitialize
1 CoreData _fetchResultSetAllocateInitialize
2 CoreData _newFetchedRowsForFetchPlan_MT
3 CoreData __executeFetchRequest
4 CoreData -[NSSQLFetchRequestContext executeRequestCore:]
5 CoreData -[NSSQLStoreRequestContext executeRequestUsingConnection:]
6 CoreData ___52-[NSSQLDefaultConnectionManager handleStoreRequest:]_block_invoke
7 CoreData ___37-[NSSQLiteConnection performAndWait:]_block_invoke
8 libdispatch.dylib __dispatch_client_callout
9 libdispatch.dylib __dispatch_lane_barrier_sync_invoke_and_complete
10 CoreData -[NSSQLiteConnection performAndWait:]
11 CoreData -[NSSQLDefaultConnectionManager handleStoreRequest:]
12 CoreData -[NSSQLCoreDispatchManager routeStoreRequest:]
13 CoreData -[NSSQLCore dispatchRequest:withRetries:]
14 CoreData -[NSSQLCore executeRequest:withContext:error:]
15 CoreData ___65-[NSPersistentStoreCoordinator executeRequest:withContext:error:]_block_invoke.657
16 CoreData -[NSPersistentStoreCoordinator _routeHeavyweightBlock:]
17 CoreData -[NSPersistentStoreCoordinator executeRequest:withContext:error:]
18 CoreData -[NSManagedObjectContext executeFetchRequest:error:]
19 HLLMQTTClient __60-[MQTTCoreDataPersistence allFlowsforClientId:incomingFlag:]_block_invoke MQTTCoreDataPersistence.m:321
20 CoreData _developerSubmittedBlockToNSManagedObjectContextPerform
21 libdispatch.dylib __dispatch_client_callout
22 libdispatch.dylib __dispatch_lane_barrier_sync_invoke_and_complete
23 CoreData -[NSManagedObjectContext performBlockAndWait:]
24 HLLMQTTClient -[MQTTCoreDataPersistence allFlowsforClientId:incomingFlag:] MQTTCoreDataPersistence.m:311
25 HLLMQTTClient -[MQTTSession checkTxFlows] MQTTSession.m:633
26 HLLMQTTClient __41-[MQTTSession decoder:didReceiveMessage:]_block_invoke MQTTSession.m:804
27 libdispatch.dylib __dispatch_client_callout
28 libdispatch.dylib __dispatch_continuation_pop$VARIANT$armv81
29 libdispatch.dylib __dispatch_source_invoke$VARIANT$armv81
30 libdispatch.dylib __dispatch_lane_serial_drain$VARIANT$armv81
31 libdispatch.dylib __dispatch_lane_invoke$VARIANT$armv81
32 libdispatch.dylib __dispatch_workloop_worker_thread
33 libsystem_pthread.dylib __pthread_wqthread

my mqtt version is the newest one . hope to fix it . thanks

[tomatobin]

Same problem