And nullable helps with null references as well as intellisense warnings.

Moreover that examples the author did are likely both oversimplified and wrong.

In the first one, a bool then a string is returned which should raise a type error in most cases (unless you do an anonymous function and feed the result back into something that accepts an object-typed parameter/use an object-typed variable to store the result).

I don't even know what's up with the second one; that's simply not valid code - if it was a normal function you cannot omit the trailing semicolon, and if it was a anonymous lambda you cannot have a trailing semicolon.