using System;

using System.Text;

public class Program

{

    public static void Main()

    {

        var sb = new StringBuilder();

        sb.Append("Start string\n");

        string? someNullableString = null;

        sb.Append(someNullableString);

        sb.Append("End String\n");

​

        Console.WriteLine(sb.ToString());

    }

}