wrapping.cs

using System;

namespace Dummy
{
    class Program
    {
        private static void Header(string title)
        {
            Console.WriteLine(new string('=', 79));
            Console.WriteLine(title);
            Console.WriteLine(new string('=', 79));
        }

        static void Main()
        {
            WrapValue<string>.DefaultValue = "missing-name";
            var withValue = new WrapValue<string>("Wouter");
            var withoutValue = new WrapValue<string>();

            Header("Without handling");
            Console.WriteLine("My name is {0}", withValue);
            Console.WriteLine("My name is {0}", withoutValue);

            Header("With handling");
            WrapValue<string>.MissingValueHandler = _ =>
                Console.WriteLine("WARNING: Returning default value because no actual value");

            Console.WriteLine("My name is {0}", withValue);
            Console.WriteLine("My name is {0}", withoutValue);

            try
            {
                Header("With exception management");
                WrapValue<string>.MissingValueHandler = _ =>
                    throw new Exception($"Returning default value because no actual value");
                Console.WriteLine("My name is {0}", withValue);
                Console.WriteLine("My name is {0}", withoutValue);
            }
            catch (Exception ex)
            {
                Console.WriteLine("Exception: " + ex);
            }

            // The downsides:
            // 1. The MissingValueHandler and Default value are static to the type and not the field but that can easily
            //    by providing a parent and a type name.
            // 2. This approach hides things from the developer that uses it, making it harder to debug (and I don't like that)
        }

        public class WrapValue<T>
        {
            public bool HasValue { get; }
            public T ActualValue { get; }
            public static T DefaultValue { get; set; } 
            public static Action<WrapValue<T>> MissingValueHandler { get; set; } = _ => { };

            public WrapValue(T value)
            {
                ActualValue = value;
                HasValue = true;
            }

            public WrapValue()
            {
                HasValue = false;
            }

            public static implicit operator WrapValue<T>(T value)
            {
                return new WrapValue<T>(value);
            }

            public static implicit operator T(WrapValue<T> d)
            {
                if (d.HasValue)
                {
                    return d.ActualValue;
                }

                MissingValueHandler(d);
                return DefaultValue;
            }

            public override string ToString()
            {
                // ReSharper disable once RedundantCast because it's not redundant since we don't want "WrapValue`1[T]"
                return ((T)this).ToString();
            }
        }
    }
}

Output:

===============================================================================
Without handling
===============================================================================
My name is Wouter
My name is missing-name
===============================================================================
With handling
===============================================================================
My name is Wouter
WARNING: Returning default value because no actual value
My name is missing-name
===============================================================================
With exception management
===============================================================================
My name is Wouter
Exception: System.Exception: Returning default value because no actual value
   at Dummy.Program.<>c.<Main>b__1_1(WrapValue`1 _) in C:\repos\Dummy\Dummy\Prog
ram.cs:line 35
   at Dummy.Program.WrapValue`1.op_Implicit(WrapValue`1 d) in C:\repos\Dummy\Dum
my\Program.cs:line 80
   at Dummy.Program.WrapValue`1.ToString() in C:\repos\Dummy\Dummy\Program.cs:li
ne 87
   at System.Text.StringBuilder.AppendFormatHelper(IFormatProvider provider, Str
ing format, ParamsArray args)
   at System.IO.StreamWriter.WriteFormatHelper(String format, ParamsArray args,
Boolean appendNewLine)
   at System.IO.StreamWriter.WriteLine(String format, Object arg0)
   at System.IO.TextWriter.SyncTextWriter.WriteLine(String format, Object arg0)
   at System.Console.WriteLine(String format, Object arg0)
   at Dummy.Program.Main() in C:\repos\Dummy\Dummy\Program.cs:line 37