#nullable enable

​

using System;

using System.Collections.Generic;

​

class BaseExpression { 

}

​

class Expression : BaseExpression { 

}

​

class X {

    public List<Expression> filters;

}

public class Program

{

    public static void Main()

    {

        BaseExpression existingFilter = new();

        if (existingFilter is not Expression) { Console.WriteLine("A"); }

    }

}