Unity-Technologies/UnityCsReference · error · ArgumentNullException

gameObjects

Error message

gameObjects

What it means

Thrown by AddGameObjectsToPrefabAndConnect when the `gameObjects` array argument is null. The method connects existing scene GameObjects into a target Prefab, so a null array is a programmer error caught as ArgumentNullException before any work begins.

Source

Thrown at Editor/Mono/Prefabs/PrefabUtility.bindings.cs:274

        [StaticAccessor("PrefabUtilityBindings", StaticAccessorType.DoubleColon)]
        extern private static GameObject ApplyPrefabInstance_Internal([NotNull] GameObject root);

        [StaticAccessor("PrefabUtilityBindings", StaticAccessorType.DoubleColon)]
        [NativeMethod(ThrowsException = true)]
        extern private static GameObject SaveAsPrefabAsset_Internal([NotNull] GameObject root, string path, out bool success);

        [StaticAccessor("PrefabUtilityBindings", StaticAccessorType.DoubleColon)]
        [NativeMethod(ThrowsException = true)]
        extern private static GameObject SaveAsPrefabAssetAndConnect_Internal([NotNull] GameObject root, string path, out bool success);

        [StaticAccessor("PrefabUtilityBindings", StaticAccessorType.DoubleColon)]
        [NativeMethod(ThrowsException = true)]
        extern private static GameObject SavePrefabAsset_Internal([NotNull] GameObject root, out bool success);

        internal static void AddGameObjectsToPrefabAndConnect(GameObject[] gameObjects, Object targetPrefab)
        {
            if (gameObjects == null)
                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");

View on GitHub (pinned to 225b0fbdb5)

Solutions

1. Pass a non-null GameObject[] even if empty (though empty throws separately).
2. Initialize arrays to empty before populating: new GameObject[0].
3. Guard the selection: if (gameObjects == null) return; or inform the user to select objects.

Example fix

// before
PrefabUtility.AddGameObjectsToPrefabAndConnect(null, target);

// after
GameObject[] gos = Selection.gameObjects ?? Array.Empty<GameObject>();
if (gos.Length == 0) return;
PrefabUtility.AddGameObjectsToPrefabAndConnect(gos, target);

if (gameObjects == null)
    gameObjects = System.Array.Empty<GameObject>();

When it happens

Trigger: Calling AddGameObjectsToPrefabAndConnect(null, targetPrefab), or passing a field/variable that was never populated (e.g. a Selection.transforms array that returned nothing and was assigned null).

Common situations: Editor tools driven by selection where nothing is selected. Arrays built via LINQ that can be null instead of empty. Refactors that removed the array population step.

Related errors

• targetPrefab
• The path is null
• gameObjects array is empty
• Target Prefab has to be a Prefab Asset
• GameObject in input 'gameObjects' array is null

AI-assisted analysis of Unity-Technologies/UnityCsReference@225b0fbdb5 (2026-08-13). Data as JSON: /api/errors/2e168fa68a1db5a8. Report an issue: GitHub.