Using C# 7 features, throw expressions & x is T y

gistfile1.cs

public Bar DoSomething(Foo uncheckedFoo) => 
    uncheckedFoo is Foo foo 
        ? DoSomething2(foo) 
        : throw new ArgumentNullException(nameof(uncheckedFoo));

private Bar DoSomething2(Foo foo) => // foo is definitely set here