Null reference when accessing GameObject in the Array(C#)

Hello! I am new to Unity and I faced a problem with arrays. I create a prefab and try to instantiate it and store instances into my array. Here's the code:

 public class TestScript : MonoBehaviour
 {    
         public Transform somePrefab;
         GameObject[] testArray;
 
         void Start ()
         {
                 testArray = new GameObject[5];
                 CreatingObjects ();
                 AssignNames ();
         }
     
         void CreatingObjects ()
         {
                 for (int i = 0; i < 5; i++) {
                         testArray [i] = Instantiate (somePrefab) as GameObject;                            
                 }
         }
 
         void AssignNames ()
         {
                 for (int i = 0; i < 5; i++)
                         testArray [i].name = "Cube # " + i;
         }
 }

Unity gives me NullReferenceException error at line 28 (23 here):

"NullReferenceException: Object reference not set to an instance of an object TestScript.AssignNames () (at Assets/Scripts/TestScript.cs:28) TestScript.Start () (at Assets/Scripts/TestScript.cs:14)"

For some reason I cannot access my stored GameObject at specific index. Unity creates 5 objects but i can't reach them.

Looks like i don't know something about Unity arrays but i cannot figure it out.