Randomly instantiate objects of an array, but each only once. The Object you want to instantiate is null.

Hello, I'm kind of new to Unity and here I just can't figure out why it gives this error in InstObstacles().

In this I am trying to instantiate groups of obstacles.

Per island I want to instantiate at most one obstacle of the same group, thats why I try to set the whole group to null and then let a non-null object be chosen for instantiation. But the only object being instantiated is always the one in SetUp().

Here is the relevant code if something is unclear I will provide more information.

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;

 public class GroupSpawner : MonoBehaviour
 {
 float yy;
 int obstaclesAmount;
 int randomDimension;
 int randomNumber;
 int noLoop;

 public GameObject a1;
 public GameObject a2;
 public GameObject a3;
 public GameObject b1;
 public GameObject b2;
 public GameObject b3;
 public GameObject c1;
 public GameObject d1;
 public GameObject e1;
 public GameObject f1;
 public GameObject g1;

 GameObject[,] Obstacles;

 private void Awake()
 {
     Obstacles = new GameObject[7,3];
 }

 void Start()
 {
     yy = yy + 10;
 }

 void Update()
 {
     SpawnGroups();
 }


 public void SpawnGroups() //set the positon and amount of obstacle spawn, call Instantiate
 {
     if ((yy - gameObject.transform.position.y) < 50)
     {
         float distance = Random.Range(3, 13);   //distance between the groups
         obstaclesAmount = Random.Range(1, 4);   //obstacles per group
         yy = yy + distance;
         SetUp();
     }
 }
 void SetUp() //include all objects, choose and instantiate random, call Instisland
 {
     GameObject[,] Obstacles = { { a1, a2, a3 }, { b1, b2, b3 }, { c1, c1,c1 }, { d1, d1, d1 }, { e1, e1, e1 }, { f1, f1, f1 }, { g1, g1, g1 } };
     randomDimension = Random.Range(0, 7);
     randomNumber = Random.Range(0,3);

     Object.Instantiate(Obstacles[randomDimension, randomNumber], new Vector3(lw.transform.position.x + 0.7f, yy, lw.transform.position.z), Quaternion.identity);
     //This gets instantiated fine
     InstObstacles();
 }
 void InstObstacles() //exclude already spawned obstacles, choose obstacle and instantiate it, repeat x times
 {
     Obstacles[randomDimension, 0] = null; Obstacles[randomDimension, 1] = null; Obstacles[randomDimension, 2] = null;
     


     randomDimension = Random.Range(0,7);
     randomNumber = Random.Range(0,3);

     Debug.Log("test " + Obstacles[1,1] + Obstacles[2,0] + Obstacles[4,0] + Obstacles[6,0]);
     //this writes just "test" in the log, which means these are all null right?

     noLoop = 100;

     while (Obstacles[randomDimension,randomNumber] == null)
     {
         randomDimension = Random.Range(0, 7);
         randomNumber = Random.Range(0, 3);

         noLoop--;
         if (noLoop == 1)
         {
             Debug.Log("infiniteWhileLoop"); //gets called every time
             break;
         }
     }

     Debug.Log(Obstacles[randomDimension, randomNumber]);
     //This writes "Null" tho

     yy = yy + 1;
 //this gives the error
     Object.Instantiate(Obstacles[randomDimension, randomNumber], new Vector3(lw.transform.position.x + 0.7f, yy, lw.transform.position.z), Quaternion.identity);

     if (obstaclesAmount > 1) //it should call the function again to instantiate another obstacle for the group if true
     {
         obstaclesAmount--;
         InstObstacles();
     }
 }
 }