役に立たない奇妙なTips ref: http://qiita.com/items/9ab9f315f935820e5c53

result

nullObject : (null)

sample.m

id nullObject = [[nil alloc] init];
NSLog("%@", nullObject);

sample2.m

Class klass = nil;
switch (condition) {
    case a:
        klass = [MyClass1 class];
        break;
    case b:
        klass = [MyClass2 class];
        break;
    default:
        klass = nil;    // なくても良い
        break;
}// end case by condition

id instance = [[klass alloc] init];
        // 以下適切な処理を