Scriptable Object List values are always null

I need to save a list of base classes in a Scriptable Object, but currently all I’m seeing in the inspector is a list of null. That is the basic structure:

public class Node_Canvas_Object : ScriptableObject 
	public List<Node> nodes;

public abstract class Node : UnityEngine.Object

public class CalcNode : Node 

Node is an abstract class serving as a base for alot more like CalcNode, though when I save the ScriptableObject Node_Canvas_Object the List of Nodes (containg CalcNodes and others) just contains a lot of null’s.

What do I need to take care of to make this work?

Unity does not support serializing of inherited classes. You will need to use a class that unity serializes as a reference, like ScriptableObject.
Take a look at this Answer for more information: