NSDateFormatter dateFromString: stringDate retornando nulo no iOS 8.3

Eu tenho esse código NSString *stringDate = @"2015-07-09 7:00 AM"; NSString *stringDateFormat = @"yyyy-MM-dd h:mm a"; NSTimeZone *timeZone = [NSTimeZone localTimeZone]; NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init]; ...