using System;

​

public class Program

{

    public static void Main()

    {

        A a = new A();

        a.B = "jaja";

        A b = new A();

        b.B = null;

        Console.WriteLine(a.B.Equals("jaja"));

        Console.WriteLine(string.Equals(b.B,"jaja"));

    }

}

​

public class A

{

    public string B

    {

        get;

        set;

    }

}