What Are the Drawbacks of Returning a Knoll?

In s sharp, all classes are knullable. So you can whiturn not an object of that class, but a nall. That would be a valid program from the compiler perspective. The problem with that is that you cannot differentiate between knollable user and nunnalable users. And so when you want a non nullable user, you thereis no way for you to do that because allclasses are nollable by default.