NullReference Error after Instantiating a Prefab

So I don´t know if I´m missing an dumb error of myself but my problem is:
I´ve got an class which deserializes a json file into a tree-structure. That part is working without an error. Now while doing this i want to create Objects of another class - we just call it "CityObject" for the moment.

Code (CSharp):

1. public class CityObject : MonoBehaviour {
2.  
3.     private GameObject gameObject;
4.  
5.     public ArrayList children;
6.  
7.     public int width;
8.  
9.  
10.     public CityObject(GameObject prefab, int newWidth)
11.     {
12.         gameObject = Instantiate(prefab);
13.         children = new ArrayList();
14.         width = newWidth;
15.     }
16. }

Depending on the Information in the json file, the GameObject should get a simple cube prefab or a flat cube prefab and instantiate it. So far so good - in the unity Scene all Objects are created, so in my example there are 5 created GameObjects - 2 flat and 3 simple cubes.

Code (CSharp):

1. public class CityBuilder : MonoBehaviour {
2.  
3.     public GameObject plane;
4.     public GameObject cube;
5.     public CityObject origin;
6.  
7.     private int maxW = 0;
8.  
9.     private ProjectView ProcessProjectData(string jsonString)
10.     {
11.         ProjectView parsejson = JsonUtility.FromJson<ProjectView>(jsonString);
12.         return parsejson;
13.     }
14.  
15.     private GameObject FindPrefab(string type)
16.     {
17.         switch (type.ToLower())
18.         {
19.             case "block": newPlane = false; return cube;
20.             case "scope": newPlane = true; return plane;
21.             default: return null;
22.         }
23.     }
24.    
25.     private CityObject CreateGameObjectFromProjectData(ProjectData projectData, CityObject cityObjectParent)
26.     {
27.      
28.         var prefab = FindPrefab(projectData.type);
29.         if (!prefab)
30.             return null;
31.  
32.  
33.         CityObject rootCityObject = new CityObject(prefab,  getSubtreeWidth(projectData));
34.  
35.        
36.         if(maxW == 0)
37.         {
38.             maxW = rootCityObject.width;
39.         }
40.         scaleObject(rootCityObject);
41.        
42.         /* * *
43.          * If an object has one or more children, then the children should execute this method on their own.
44.          */
45.  
46.         if (projectData.children != null)
47.         {
48.             foreach (ProjectData data in projectData.children)
49.             {
50.                 Debug.Log(data.id);
51.             }
52.             foreach (ProjectData data in projectData.children)
53.             {
54.                 CityObject newChild = CreateGameObjectFromProjectData(data, rootCityObject);
55.                 rootCityObject.appendChild(newChild);
56.             }
57.         }
58.         return rootCityObject;
59.     }

The problem is that in line 40 i want to scale the gameObject of the cityObject like this:

private void scaleObject(CityObject node)

    {

        float scaleRatio = (float)(node.width/maxW);

        node.gameObject.transform.localScale.Set(scaleRatio, scaleRatio, scaleRatio);

    }

Then there is a NullReference Error for the node.GameObject - so there seems to be no reference between the cityObject and the GameObject. This is the part i can´t understand. Is it the Instantiate in the CityObejct Constructor? Isn´t the Instantiate creating a Reference between the "Script-Object" and the Gameobject in the unity-Scence?

 

Nevermind, I was wrong. Sorry :-D