Changing by ref a class passed in function

[Zaher Dirkey via Digitalmars-d-learn]

See example bellow, i want to pass object to function nullIt and 
want this function to null it.

----
import std.stdio;

static if (!is(typeof(writeln)))
	alias writefln writeln;


class MyClass{
	
}

void nullIt(ref Object o)
{
	o = null;
}

void main()
{
	auto o = new MyClass();
	
	nullIt(o);
	
	if (o is null)
		writeln("It is null");
}

Thanks in advance.