Struct variable of type struct array initializing

Im having an issue with my struct. Im working on a implementation of the Monte Carlo Tree Search and i
created a struct called Node which has specific variables.
Now i need to store parent as well as child objects of type node. Since a node can be a parent for other nodes, but also child of a node this is important.

Code (csharp):

1.  
2. System.Serializable]
3.     public struct Node
4.     {
5.  
6.         public Transform[,] CurrentField_V;
7.         public Transform[,] CurrentField_H;
8.         public Transform[,] CurrentField_Boxes;
9.         public Node [] nodeChildren;
10.         public Node [] parent;
11.         public int result;
12.         public bool isTerminal;
13.         public bool alreadyChecked;
14.         public int y;
15.         public int x;
16.         public int visitTimes;
17.  
18.  
19.  
20. //THIS IS WERE THE ISSUE IS
21.  
22.  public Node Expand(Node v)
23.     {
24.        
25.         Debug.Log("Start EXPANSION");
26.         //create a new node
27.         Node newNode = new Node();
28.         newNode.parent[0] = v; //---------> NULL REFERENCE EXCEPTION
29.         newNode.CurrentField_V = v.CurrentField_V;
30.         newNode.CurrentField_H = v.CurrentField_H;
31.         v.nodeChildren[counter] = newNode;//---------> NULL REFERENCE EXCEPTION
32.         newNode.visitTimes++;
33.  
34.  
35.     }
36.  
37.  

does anyone have a clue how i can solve this issue?

 

A few thoughts:
- Why would you use a struct for a Node instead of a class? (With a class you can you inheritance to force and implementation of Expand. That way you can decouple the MCTS logic from the actual search space.)
- Why use an array for parent? There should only be one parent.
- Expand should have no parameters and (optionally) no return type. It should expand itself into nodeChildren. (And optionally return that array.)
- Make things easier for yourself by using a List<Node> for the children instead of an array.