DestroyImmediate in Prefab Mode

I am having an editor code that have inconsistent behavior.

Code (CSharp):

1.  
2.     private void ClearAllDecosInternal()
3.     {
4.         GetAllWalls();
5.  
6.         for (int i = 0; i < _wallsInLevel.Count; i++)
7.         {
8.             /*
9.              * Inconsistent behaviour -_-
10.             if (PrefabUtility.IsPartOfPrefabInstance(_wallsInLevel[i].transform.parent.gameObject))
11.             {
12.                 PrefabUtility.UnpackPrefabInstance(_wallsInLevel[i].transform.parent.gameObject, PrefabUnpackMode.OutermostRoot, InteractionMode.AutomatedAction);
13.             }
14.             */
15.             _wallsInLevel[i].GetComponent<WallScript>().ClearAllDecorations();
16.         }
17.  
18.         MarkChangesToPrefab();
19.     }
20.  

Code (CSharp):

1.  
2.     public void ClearAllDecorations()
3.     {
4.         Transform[] childs = gameObject.GetComponentsInChildren<Transform>();
5.         List<GameObject> decos = new List<GameObject>();
6.         for (int i = 0; i < childs.Length; i++)
7.         {
8.             if (childs[i].CompareTag("WallDeco"))
9.             {
10.                 decos.Add(childs[i].gameObject);
11.             }
12.         }
13.  
14.         for (int i = 0; i < decos.Count; i++)
15.         {
16.             if (decos != null)
17.             {
18.                 DestroyImmediate(decos[i].gameObject);
19.             }
20.         }
21.     }
22.  

It works for some of prefabs and breaks for some prefabs.
The error thrown by editor is

InvalidOperationException: Destroying a GameObject inside a Prefab instance is not allowed.

.

To answer a few questions, the walls are prefabs. The Decorations are prefab. My issue is why it works on some prefabs, and not on another. I dont want to unpack the prefab because, i want to be able to use the nested prefab feature.

 

I used a workaround that worked for me.

PrefabUtility.RevertPrefabInstance