How to initialize a variable of type Interface as empty?

[Elad]

   public Package(Priority priority, Address senderAddress, Address destinationAdress)
        {
            PackageID = count++;
            Priority = priority;
            Tracking = new List<Tracking>();
            SenderAddress = senderAddress;
            DestinationAddress = destinationAdress;
             //The null is painted green,
            AddTracking(null);
          
        }

        public void AddTracking(INode node, Status status = Status.CREATION)
        {
            Tracking.Add(new Tracking(MainOffice.Clock, node, status));
        }
//And Interface
    public interface INode
    {
        void CollectPackage(Package pack);
        void DeliverPackage(Package pack);
        string GetName();
        void Work();
    }

I get such a warning "Cannot convert null literal to non-nullable reference type."
By the way in java interface can be set to null why in c # it does not work in this logic?

 

[JohnH]

Nullable reference types - C#

This article provides an overview of nullable reference types. Learn how the feature provides safety against null reference exceptions, for new and existing projects.

docs.microsoft.com

When nullable context is enabled you have mark the reference type as nullable by appending ? if it should allow nulls. For example INode?

 

[Skydiver]

Which version of C# are you using? Newer versions have nullable type checking enabled by default so you have to explicitly decorate the type to allow nulls.

 

[Elad]

Newer versions have nullable type checking enabled by default so you have to explicitly decorate the type to allow nulls.

I'm using the new Visual Studio 2022, so its default is .net Framework 6
But I did not understand what it means to "decorate" Can you give an example that I will understand?

 

[Skydiver]

See post #3.