Add an Object to a List which is part of an array does not work.

I have the problem, that i want to add objects to a list which is part of an array. i was searching in the forum, but could not find a correct solution, because mostly the problem was in the instantiating of the list and that is what i have done correct(as far as i can say):

the error comes in line 27 of the 2nd part of code.

so here is the part of my code that makes the problem:

 public class PlaygroundCreatorWorkingConcept : MonoBehaviour
 {
     public int height;
     public int width;
    
     List<WallInformation> WallInformations = new List<WallInformation>();
     List<WallInformation>[,] WallInformationSmall;
 }
 
  public class WallInformation
     {
         public Coord coordinate;
         public bool isWall;
         public float floorHeight;
         public float ceilingHeight;
 
         public WallInformation(Coord newCoordinate, bool newIsWall, float newFloorHeight, float newCeilingHeight)
         {
             coordinate = newCoordinate;
             isWall = newIsWall;
             floorHeight = newFloorHeight;
             ceilingHeight = newCeilingHeight;
         }
     }
 
 
 void Awake()
     {
    WallInformationSmall = new List<WallInformation>[width / 10, height / 10];
         for(int i = 0; i >= width / 10; i++)
         {
             for (int j = 0; j >= height / 10; j++)
             {
                 WallInformationSmall[i, j] = new List<WallInformation>();
             }
         }
      }

this is the top of the programm with all important thing for the question

  public void SetWallInformations()
     {
         for (int x = 0; x < width; x++)
         {
             for (int z = 0; z < height; z++)
             {
                 WallInformations.Add(new WallInformation(new Coord(x, z), isWall[x, z], floorWorld[x, z], ceilingWorld[x, z]));
             }
         } //scheint bis hier zu funktionieren, da er bei small 50*50 = 2500 informationen füllt.
         foreach (WallInformation WallInformation in WallInformations)
         {
             Debug.Log(WallInformations.Count);
             Debug.Log(WallInformation.coordinate.tileX);
             Debug.Log(WallInformation.coordinate.tileZ);
             Debug.Log(WallInformation.isWall);
             Debug.Log(WallInformation.floorHeight);
             Debug.Log(WallInformation.ceilingHeight);
             int i = 0;
             int j = 0;
             if (WallInformation.coordinate.tileX >= i + 0 && WallInformation.coordinate.tileX <= i + 10)
             {
                 Debug.Log("Bin Hier1.");
 
                 if (WallInformation.coordinate.tileZ >= j + 0 && WallInformation.coordinate.tileZ <= j + 10)
                 {
                     Debug.Log("Bin Hier2.");
                     WallInformationSmall[i, j].Add(WallInformation);
                 }
                 else
                 {
                     j++;
                     //return;
                     Debug.Log("Bin Hier3.");
                 }
             }
             else
             {
                 i++;
                 j = 0;
                 //return;
             }
             i = 0;
             Debug.Log("Bin Hier4.");
 
         }
    }

the problem is that the line below Debug.Log(“Bin Hier2”); does give me this error:

NullReferenceException: Object reference not set to an instance of an object

@NoDumbQuestion

Is this because it is not possible to make an array of lists how I tried at the top, or what am I doing wrong that it is not working as I for my understanding would expect?
The thing is when I work with it, it always behaves like I wanted, there is no red underline or something, just when I want to run it it has the error.

I think i got some kind of an answer, to my question, or at least i got the solution to the problem i was thinking of.

the problem was to make an array of lists, and how it is working, or add items to it.

and the solution was pretty easy.

List<int>[] myList;

void Start()
{
myList = new List<int>[sizeOfArrayOfLists];

for (int i = 0; int < sizeOfArrayOfLists; i++)
{
myList *= new List<int>();*

}
}
just wanted to share, if someone has the same problem. if i come across something that does not work with this, I will edit here.