C#中烦人的Null值判断竟然这样就被消灭了

public void DoSomething(string message)
{
  if(message == null)
    throw new ArgumentNullException();
    
    // ...
}

public void DoSomething(string message)
{
  Assert.That<ArgumentNullException>(message == null, nameof(DoSomething));
    // ...
}

public void DoSomething([NotNull]string message) // Does not affect anything at runtime.
{
}

public void AnotherMethod()
{
  DoSomething(null); // MsBuild doesn't allow to build.
  string parameter = null;
  DoSomething(parameter); // MsBuild allows build. But nothing happend at runtime.
}

public class NotNull<T>
{
    public NotNull(T value)
    {
        this.Value = value;
    }

    public T Value { get; set; }

    public static implicit operator NotNull<T>(T value)
    {
        if (value == null)
            throw new ArgumentNullException();
        return new NotNull<T>(value);
    }
}

static void Main(string[] args)
{
  DoSomething("Hello World!"); // Works perfectly ?
  
  DoSomething(null); // Throws ArgumentNullException at runtime.
  
  string parameter = null;
  DoSomething(parameter); // Throws ArgumentNullException at runtime.
}

public static void DoSomething(NotNull<string> message) // <--- NotNull is used here
{
    Console.WriteLine(message.Value);
}

public void DoSomething(NotNull<string> message, NotNull<int> id, NotNull<Product> product)
{
  // ...
}