Unity-Technologies/UnityCsReference · error · ArgumentException

GameObject in input 'gameObjects' array is null

Error message

GameObject in input 'gameObjects' array is null

What it means

Thrown inside the AddGameObjectsToPrefabAndConnect loop when an individual element `go` in the gameObjects array is null. Each array element is null-checked before any prefab logic runs on it, so a single null entry aborts the whole operation.

Source

Thrown at Editor/Mono/Prefabs/PrefabUtility.bindings.cs:292

                throw new ArgumentNullException("gameObjects");

            if (gameObjects.Length == 0)
                throw new ArgumentException("gameObjects array is empty");

            if (targetPrefab == null)
                throw new ArgumentNullException("targetPrefab");

            if (!PrefabUtility.IsPartOfPrefabAsset(targetPrefab))
                throw new ArgumentException("Target Prefab has to be a Prefab Asset");

            Object targetPrefabInstance = null;

            var targetPrefabObject = PrefabUtility.GetPrefabAssetHandle(targetPrefab);

            foreach (GameObject go in gameObjects)
            {
                if (go == null)
                    throw new ArgumentException("GameObject in input 'gameObjects' array is null");

                if (EditorUtility.IsPersistent(go))  // Prefab asset
                    throw new ArgumentException("Game object is part of a prefab");

                var parentPrefabInstance = GetParentPrefabInstance(go);
                if (parentPrefabInstance == null)
                    throw new ArgumentException("GameObject is not (directly) parented under a target Prefab instance.");

                if (targetPrefabInstance == null)
                {
                    targetPrefabInstance = parentPrefabInstance;
                    if (!IsPrefabInstanceObjectOf(go.transform.parent, targetPrefabObject))
                        throw new ArgumentException("GameObject is not parented under a target Prefab instance.");
                }
                else
                {
                    if (parentPrefabInstance != targetPrefabInstance)
                    {

View on GitHub (pinned to 225b0fbdb5)

Solutions

1. Filter nulls before calling: gos = gos.Where(g => g != null).ToArray().
2. Ensure no destroyed/null references are added to the list.
3. Validate each element in a loop and report which index was null for debugging.

Example fix

// before
GameObject[] gos = Selection.gameObjects; // may contain nulls from editor state
PrefabUtility.AddGameObjectsToPrefabAndConnect(gos, target);

// after
GameObject[] gos = Selection.gameObjects.Where(g => g != null).ToArray();
PrefabUtility.AddGameObjectsToPrefabAndConnect(gos, target);

gameObjects = gameObjects.Where(g => g != null).ToArray();

When it happens

Trigger: An array containing a null slot, e.g. from Selection.transforms converted to GameObjects where a transform was missing, a List with Add(null), or an array sized larger than its filled entries.

Common situations: Building the array from destroyed objects, Find calls returning null, mixed valid/invalid selection, or LINQ that preserves nulls. Arrays pre-allocated with `new GameObject[n]` then partially filled.

Related errors

• gameObjects
• gameObjects array is empty
• targetPrefab
• Target Prefab has to be a Prefab Asset
• Game object is part of a prefab

AI-assisted analysis of Unity-Technologies/UnityCsReference@225b0fbdb5 (2026-08-13). Data as JSON: /api/errors/bd7e93ea5e9b60ac. Report an issue: GitHub.