Can you put this early return together with the definition of `knownDynamicSubclass` and make it a one liner? And add a comment on it's purpose?

```objc
Class knownDynamicSubclass = objc_getAssociatedObject(self, RACSubclassAssociationKey);
if (knownDynamicSubclass != nil) return knownDynamicSubclass;
```

Also, we should compare to `Nil` technically.