NSInvalidArgumentException Unacceptable type of value for attribute: property; desired type = NSString; given type = NSNull; value = <null>

Question

Problem: when assigning the null value to a property it gives error: desired type = NSString; given type =null.

Recieving this value from NSDictionary *logBookClass = [json objectForKey:LOG_BOOK]; And when the value is null the app crashes giving following error:

Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Unacceptable type of value for attribute: property = "logbook_name"; desired type = NSString; given type = NSNull; value = .'

Following code is used:

LogBook *lBook = [NSEntityDescription
                      insertNewObjectForEntityForName:LOG_BOOK
                      inManagedObjectContext:context];
    lBook.logbook_id = [NSNumber numberWithInt:[[logBookClass objectForKey:LOGBOOK_ID] intValue]];
    lBook.logbook_name = [logBookClass objectForKey:LOGBOOK_NAME];

Following is the callstack

Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Unacceptable type of value for attribute: property = >"logbook_name"; desired type = NSString; given type = NSNull; value = <null>.'
 *** First throw call stack:
 (
    0   CoreFoundation                      0x00007fff20406d44 __exceptionPreprocess + 242
    1   libobjc.A.dylib                     0x00007fff201a4a65 objc_exception_throw + 48
    2   CoreData                            0x00007fff25bd52a6 _PFManagedObject_coerceValueForKeyWithDescription + 2148
    3   CoreData                            0x00007fff25bdcbc8 _sharedIMPL_setvfk_core + 178
    4   Npalm                               0x000000010fa822c7 -[NpLoginViewController addData:] + 2583
    5   Npalm                               0x000000010fa8182b __50-[NpLoginViewController sendAuthenticateRequest::]_block_invoke + 331
    6   CFNetwork                           0x00007fff23e39a92 CFNetwork + 31378
    7   CFNetwork                           0x00007fff23e55118 _CFHTTPMessageSetResponseProxyURL + 16297
    8   libdispatch.dylib                   0x000000010fee0816 _dispatch_call_block_and_release + 12
    9   libdispatch.dylib                   0x000000010fee1a5b _dispatch_client_callout + 8
    10  libdispatch.dylib                   0x000000010fef0325 _dispatch_main_queue_drain + 1169
    11  libdispatch.dylib                   0x000000010feefe86 _dispatch_main_queue_callback_4CF + 31
    12  CoreFoundation                      0x00007fff20373261 __CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__ + 9
    13  CoreFoundation                      0x00007fff2036da56 __CFRunLoopRun + 2761
    14  CoreFoundation                      0x00007fff2036ca90 CFRunLoopRunSpecific + 562
    15  GraphicsServices                    0x00007fff2cb72c8e GSEventRunModal + 139
    16  UIKitCore                           0x00007fff2508e90e -[UIApplication _run] + 928
    17  UIKitCore                           0x00007fff25093569 UIApplicationMain + 101
    18  Npalm                               0x000000010fadd618 main + 104
    19  dyld                                0x000000010fe56f21 start_sim + 10
    20  ???                                 0x000000011b12b51e 0x0 + 4749178142
 )

What should be done to handle null value.