How to make a non-nullable type wrapper in C#, today… (doesn't work, for blog)

Example.cs

public void DoStuff(object input)
{
  if (input == null)
    throw new ArgumentNullException("input");

  // Method implementation...
}

NonNull_Classic.cs

public struct NonNull<T> where T : class
{
  private readonly T _value;
  public T Value { get { return _value; } }

  public NonNull(T instance)
  {
    if (instance == null)
    throw new ArgumentNullException("instance", "The \"instance\" parameter must not be null.");

    _value = instance;
  }

  public override int GetHashCode()
  {
    return _value.GetHashCode();
  }

  public override bool Equals(object obj)
  {
    return _value.Equals(obj);
  }

  public static bool operator ==(NonNull<T> valueA, NonNull<T> valueB)
  {
    return valueA._value == valueB._value;
  }

  public static bool operator !=(NonNull<T> valueA, NonNull<T> valueB)
  {
    return valueA._value != valueB._value;
  }

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

  public static explicit operator T(NonNull<T> value)
  {
    return value._value;
  }
}

NonNull_NoDefaultConstructor.cs

public struct NonNull<T> where T : class
{
  private readonly T _value;
  public T Value { get { return _value; } }

  [Obsolete("The default parameterless constructor has been disabled please use NonNull<T>(T instance) constructor instead.", true)]
  public NonNull(object dummy)
  {
    throw new NotSupportedException("The default parameterless constructor has been disabled please use NonNull<T>(T instance) constructor instead.");
  }

  public NonNull(T instance)
  {
    if (instance == null)
    throw new ArgumentNullException("instance", "The \"instance\" parameter must not be null.");

    _value = instance;
  }

  public override int GetHashCode()
  {
    return _value.GetHashCode();
  }

  public override bool Equals(object obj)
  {
    return _value.Equals(obj);
  }

  public static bool operator ==(NonNull<T> valueA, NonNull<T> valueB)
  {
    return valueA._value == valueB._value;
  }

  public static bool operator !=(NonNull<T> valueA, NonNull<T> valueB)
  {
    return valueA._value != valueB._value;
  }

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

  public static explicit operator T(NonNull<T> value)
  {
    return value._value;
  }
}