using System;

using System.Xml.Serialization;

public class Program

{

    public static void Main()

    {

        var obj = new SomeType { value = 99 };

        var serializer = new System.Xml.Serialization.XmlSerializer(obj.GetType());

        serializer.Serialize(Console.Out, obj);

        //Console.WriteLine("Hello World");

    }

}

​

public class SomeType

{

    private System.Nullable<decimal> valueField1;

    [XmlElementAttribute(Form=System.Xml.Schema.XmlSchemaForm.Unqualified, IsNullable=true)]

    public System.Nullable<decimal> value {

        get {

            return this.valueField1;

        }

        set {

            this.valueField1 = value;

        }

    }

}