using System;

public class Program

{

    public static void Main()

    {

        Foo foo = null;

        DoubleNegative(foo);

        Proposed(foo);

        Console.WriteLine();

        foo = new Foo();

        DoubleNegative(foo);

        Proposed(foo);

        Console.WriteLine();

        foo.Bar = "Hello";

        DoubleNegative(foo);

        Proposed(foo);

    }

    private static void DoubleNegative(Foo foo)

    {

        Console.WriteLine("Double negative: " + (foo is not { Bar: not null }));

    }

    private static void Proposed(Foo foo)

    {

        Console.WriteLine("Proposed: " + (foo is { Bar: null }));

    }

}

​

public class Foo

{

    public string Bar { get; set; }

}

​