dogs.m

NSDictionary *dogBreeds = @{@”Bugsy” : @”Pug”,
                            @”Marcelle” : @”Chow Chow”,
                            @”Daisy” : @”Labrador”;
NSString *name = @"Chloe's breed is: ";
NSString *breed = dogBreeds[@"Chloe"];
/* Crash at runtime because breed is null */
NSString *message = [name stringByAppendingString:breed];