static void Main(string[] args)
        {
            ReferenceTest referenceTest = new ReferenceTest(99);

            Console.WriteLine(referenceTest.data);

            ReferenceTest.NullTest(ref referenceTest);
            if (referenceTest == null)
            {
                Console.WriteLine("null");
            }
            else
            {
                Console.WriteLine(referenceTest.data);
            }
        }
 public static void NullTest(ref ReferenceTest referenceTest)
 {
     referenceTest = null;
 }