Я получаю эти данные от веб-служб JSON

List ARRAY: (
    {
    assets =         (
                    {
            identity = 34DL3611;
            systemId = 544507;
        },
                    {
            identity = 34GF0512;
            systemId = 5290211;
        },
                    {
            identity = 34HH1734;
            systemId = 111463609;
        },
                    {
            identity = 34HH1736;
            systemId = 111463622;
        },
                    {
            identity = 34YCJ15;
            systemId = 294151155;
        }
    );
    identity = DEMO;
    systemId = 4921244;
})

Используя этот код:

NSArray *list =[NSJSONSerialization JSONObjectWithData:data options:kNilOptions error:&error];

NSLog(@"Response data: %@", responseString);

NSLog(@"List ARRAY: %@", list);

NSDictionary *dict = [list objectAtIndex: 0];

NSMutableArray *vehicleGroups = [dict objectForKey:@"identity"];

NSLog(@"Vehicle Groups: %@", vehicleGroups);

Вот код выбора, который я использую:

    -(NSInteger)numberOfComponentsInPickerView:(UIPickerView *)pickerView{
return 1;}

- (NSInteger)pickerView:(UIPickerView *)pickerView numberOfRowsInComponent :(NSInteger)component { 
return [vehicleGroups count];}

-(NSString *)pickerView:(UIPickerView *)pickerView titleForRow:(NSInteger)row forComponent:(NSInteger)component{return nil;}

-(void)pickerView:(UIPickerView *)pickerView didSelectRow:(NSInteger)row inComponent:(NSInteger)component{
 }

Приложение вылетает на линии

return [vehicleGroups count];

метод делегатаnumberOfRowsInComponent изpickerView, Я не понимаю, почему я сталкиваюсь с этой проблемой?

//Код////

    NSArray *list =[NSJSONSerialization JSONObjectWithData:data options:kNilOptions error:&error];

NSLog(@"Response data: %@", responseString);

NSLog(@"List ARRAY: %@", list);

NSDictionary *dict = [list objectAtIndex: 0];

vehicleList = [dict objectForKey: @"assets"];

self.vehicleGroups = [[NSMutableArray alloc] init];

vehicleGroups = [dict objectForKey:@"identity"];

NSLog(@"Vehicle Groups: %@", vehic,leGroups);

NSString *identity = [dict objectForKey: @"identity"];

NSString *systemid = [dict objectForKey:@"systemId"];

self.listVehicles = [[NSMutableArray alloc] init];

self.listVehiclesID =[[NSMutableArray alloc]init];

NSLog(@"GroupOfVehicles: %@", groupOfVehicles);

for (NSUInteger index = 0; index < [vehicleList count]; index++) {

    itemDict = [vehicleList objectAtIndex: index];

    [self.listVehicles addObject:[itemDict objectForKey:@"identity"]];

    [self.listVehiclesID addObject:[itemDict objectForKey:@"systemId"]];
}

NSLog(@"Group Name: %@", identity);

NSLog(@"Assets: %@", listVehicles);

NSLog(@"Assets System ID: %@", listVehiclesID);

NSLog(@"GroupSystemID: %@", systemid);