Attach an Image to an Object Loader

gistfile1.m

[[RKObjectManager sharedManager] postObject:contact delegate:self block:^(RKObjectLoader* loader) {
    RKObjectMapping* serializationMapping = [[[RKObjectManager sharedManager] mappingProvider] serializationMappingForClass:[Contact class]];
    NSError* error = nil;
    NSDictionary* dictionary = [[RKObjectSerializer serializerWithObject:contact mapping:serializationMapping] serializedObject:&error];
    RKParams* params = [RKParams paramsWithDictionary:dictionary];
    [params setData:[contact avatarImageData] MIMEType:@"image/png" forParam:@"avatar_image"];
    loader.params = params;
}];

NSDictionary* dictionary = [[[RKObjectSerializer serializerWithObject:contact] mapping:serializationMapping] serializedObject:&error];

Should be

NSDictionary* dictionary = [[RKObjectSerializer serializerWithObject:contact mapping:serializationMapping] serializedObject:&error];

forParams:@"avatar_image"
should read
forParam:@"avatar_image"
(without the s)