A sample program for Stack Overflow question 34111695 (http://stackoverflow.com/q/34111695/19818)

Program.cs

// See: http://stackoverflow.com/q/34111695/19818

namespace StackOverflow34111695
{
    using System;
    using System.IO;
    using System.Xml;
    using System.Xml.Schema;
    using System.Xml.Serialization;

    public struct Maybe<T> : IXmlSerializable where T : class
    {
        public readonly T _value;

        public Maybe(T value)
        {
            _value = value;
        }

        public override string ToString()
        {
            if (_value == null)
            {
                return "None";
            }
            return string.Format("Some({0})", _value);
        }

        XmlSchema IXmlSerializable.GetSchema() { return null; }

        void IXmlSerializable.ReadXml(XmlReader reader)
        {
            var value = (T)reader.ReadElementContentAs(typeof(T), null);
            var maybe = new Maybe<T>(value);
            this = maybe;
        }

        void IXmlSerializable.WriteXml(XmlWriter writer)
        {
            if (_value == null)
            {
                // I want to emit nothing
            }
            else
            {
                writer.WriteValue(_value);
            }
        }
    }

    [XmlRoot("SomeObject")]
    public class SomeObjectV1
    {
        public string MaybeAString { get; set; }
    }

    [XmlRoot("SomeObject")]
    public class SomeObjectV2
    {
        public Maybe<string> MaybeAString { get; set; }
    }

    class Program
    {
        static void Main(string[] args)
        {
            var obj = new SomeObjectV2 { MaybeAString = new Maybe<string>(null) };
            Console.WriteLine("ORIGINAL PROPERTY VALUE: <{0}>", obj.MaybeAString);
            Console.WriteLine();

            // V2 of the app serializes a value
            var serializerV2 = new XmlSerializer(typeof(SomeObjectV2));
            var writer = new StringWriter();
            serializerV2.Serialize(writer, obj);
            var serialized = writer.ToString();

            Console.WriteLine("SERIALIZED VALUE:");
            Console.WriteLine(serialized);
            Console.WriteLine();

            // V1 of the app deserializes the value
            var serializerV1 = new XmlSerializer(typeof(SomeObjectV1));
            var reader = new StringReader(serialized);
            var deserialized = (SomeObjectV1)serializerV1.Deserialize(reader);

            Console.WriteLine("DESERIALIZED PROPERTY: <{0}>", deserialized.MaybeAString);
            Console.WriteLine(deserialized.MaybeAString == null ? "Yay! It worked!" : "It's an empty string, not null :(");
            Console.WriteLine();
            Console.WriteLine("Press any key to exit.");
            Console.ReadKey();
        }
    }
}