a test from wiziq.com - secocnd question

cs_online_test_02_nullable.cs

/* Question 2 of a C# Test
  http://www.wiziq.com/online-tests/14096-csharp-your-skills-1
  
  ref Convert.ToString:
  https://msdn.microsoft.com/en-us/library/astxcyeh(v=vs.110).aspx
  Quote:
  Return Value
    Type: System.String
    The string representation of value, or String.Empty if value is an object
    whose value is null. If value is null, the method returns null.

  Object.ToString() : System.NullReferenceException
*/

using System;
using System.Collections.Generic;

class Solution {
  static void Main(string[] args) {
    object obj = null;
    string strobj = obj.ToString();
    string objstr = Convert.ToString(obj);

  }
}