Call a GET method with RestKit v0.20 and rmap the results

gistfile1.m

        RKLogConfigureByName("RestKit/Network", RKLogLevelTrace);
        RKLogConfigureByName("RestKit/ObjectMapping", RKLogLevelTrace);
        
        //NSString *url = @"http://0.0.0.0:5001/";
        NSString *url = @"https://asteroids-nemesis.herokuapp.com/";
        
        NSURL *baseURL = [NSURL URLWithString:url];
        
        AFHTTPClient * client = [AFHTTPClient clientWithBaseURL:baseURL];
        [client setDefaultHeader:@"Accept" value:RKMIMETypeJSON];
        
        _restKitObjectManager = [[RKObjectManager alloc] initWithHTTPClient:client];
        [_restKitObjectManager.HTTPClient setDefaultHeader:@"some-custom-header" value:@"ABC"];
        [_restKitObjectManager setRequestSerializationMIMEType:RKMIMETypeJSON];
        
        RKObjectMapping *gamerMapping = [RKObjectMapping mappingForClass:[Player class]];
        [gamerMapping addAttributeMappingsFromDictionary:@{
         @"username" : @"username",
         @"score" : @"score"
         }];
        
        RKResponseDescriptor *responseDescriptor = [RKResponseDescriptor responseDescriptorWithMapping:gamerMapping pathPattern:nil keyPath:@"leaderboard" statusCodes:RKStatusCodeIndexSetForClass(RKStatusCodeClassSuccessful)];
        [_restKitObjectManager addResponseDescriptor:responseDescriptor];
        
    NSString *path = [NSString stringWithFormat:@"highscores/%i/%i", fromRank, toRank];
    
    //Call the webservice
    [_restKitObjectManager getObjectsAtPath:path parameters:nil
                            success:^(RKObjectRequestOperation * operation, RKMappingResult *mappingResult)
     {
         //NSLog(@"success: mappings: %@", mappingResult);
         NSArray *result = [mappingResult array];
         
         //Call the delegate with the results
         [_delegate loadHighscoresResult:result];
     }
         failure:^(RKObjectRequestOperation * operaton, NSError * error)
     {
         NSLog (@"failure: operation: %@ \n\nerror: %@", operaton, error);
     }];