Unity-Technologies/UnityCsReference · error · ArgumentNullException

instanceRoot

Error message

instanceRoot

What it means

PrefabUtility.UnpackPrefabInstance throws an ArgumentNullException when instanceRoot is null. This method unpacks a prefab instance back into regular GameObjects and requires the root GameObject of the prefab instance.

Source

Thrown at Editor/Mono/Prefabs/PrefabUtility.cs:2765

        }

        [RequiredByNativeCode]
        internal static void Internal_CallPrefabInstanceReverted(GameObject instanceRoot)
        {
            Assert.IsNotNull(instanceRoot);

            prefabInstanceReverted?.Invoke(instanceRoot);
        }

        [AutoStaticsCleanupOnCodeReload]
        public static event Action<GameObject, PrefabUnpackMode> prefabInstanceUnpacking;
        [AutoStaticsCleanupOnCodeReload]
        public static event Action<GameObject, PrefabUnpackMode> prefabInstanceUnpacked;

        public static void UnpackPrefabInstance(GameObject instanceRoot, PrefabUnpackMode unpackMode, InteractionMode action)
        {
            if (instanceRoot == null)
                throw new ArgumentNullException(nameof(instanceRoot));

            if (!IsPartOfNonAssetPrefabInstance(instanceRoot))
                throw new ArgumentException("UnpackPrefabInstance must be called with a Prefab instance.");

            if (!IsOutermostPrefabInstanceRoot(instanceRoot))
                throw new ArgumentException("UnpackPrefabInstance must be called with a root Prefab instance GameObject.");

            if (action == InteractionMode.UserAction)
            {
                var undoActionName = "Unpack Prefab instance";
                Undo.RegisterFullObjectHierarchyUndo(instanceRoot, undoActionName);
                var newInstanceRoots = UnpackPrefabInstanceAndReturnNewOutermostRoots(instanceRoot, unpackMode);
                foreach (var newInstanceRoot in newInstanceRoots)
                {
                    var prefabInstance = PrefabUtility.GetPrefabInstanceHandle(newInstanceRoot);
                    if (prefabInstance)
                    {
                        Undo.RegisterCreatedObjectUndo(prefabInstance, undoActionName);

View on GitHub (pinned to 225b0fbdb5)

Solutions

1. Null-check instanceRoot before calling.
2. Verify the GameObject reference is valid using Unity's null comparison (handles destroyed objects).
3. Trace the source of instanceRoot to ensure it comes from a valid prefab instance lookup.

Example fix

// before
PrefabUtility.UnpackPrefabInstance(maybeNullGo, PrefabUnpackMode.OutermostRoot, InteractionMode.UserAction);
// after
if (instanceRoot != null)
    PrefabUtility.UnpackPrefabInstance(instanceRoot, PrefabUnpackMode.OutermostRoot, InteractionMode.UserAction);

if (instanceRoot != null)
    PrefabUtility.UnpackPrefabInstance(instanceRoot, PrefabUnpackMode.OutermostRoot, InteractionMode.UserAction);

static bool IsValidInstanceRoot(GameObject go) => go != null;

When it happens

Trigger: Calling PrefabUtility.UnpackPrefabInstance(null, unpackMode, action) where the first argument is null.

Common situations: Passing a destroyed GameObject, a reference that was set to null by a previous operation, or a field populated from a failed lookup (e.g., GetPrefabInstanceHandle returned null).

Related errors

• plainGameObjects
• GameObject is null.
• Prefab Asset path is null or empty
• plainGameObjects has no objects
• plainGameObjects has a null GameObject

AI-assisted analysis of Unity-Technologies/UnityCsReference@225b0fbdb5 (2026-08-13). Data as JSON: /api/errors/7583f2024baff562. Report an issue: GitHub.