C# quiz #2: objects, strings, null

this is a continuation from the previous quiz; given this class definition:

public class Foo {
    public void Bar(object x) {
        Console.WriteLine("object x was called");
    }
    public void Bar(string x) {
        Console.WriteLine("string x was called");
    }
}

what will be output to the console with the following code:

Foo f = new Foo();
try {
    f.Bar(null);
}
catch {
    Console.WriteLine("no method was called");
}

Extra points for explaining why