What causes "Cannot apply added component. Component is null." in Unity-Technologies/UnityCsReference?

Null-check before calling: if (component == null) return;

Unity-Technologies/UnityCsReference · error · ArgumentNullException

Cannot apply added component. Component is null.

Error message

Cannot apply added component. Component is null.

What it means

Thrown by ApplyAddedComponent(Component, string, InteractionMode) when component is null — ArgumentNullException(nameof(component)). The method dereferences component immediately (IsAddedComponentOverride, gameObject access), so null is rejected with an explanatory message.

Source

Thrown at Editor/Mono/Prefabs/PrefabUtility.cs:1168

        {
            if (originalComponentOrder.Length != newComponentOrder.Length)
                return true;

            for (int i = 0; i < originalComponentOrder.Length; ++i)
            {
                if (originalComponentOrder[i] != newComponentOrder[i])
                    return true;
            }

            return false;
        }

        public static void ApplyAddedComponent(Component component, string assetPath, InteractionMode action)
        {
            DateTime startTime = DateTime.UtcNow;

            if (component == null)
                throw new ArgumentNullException(nameof(component), "Cannot apply added component. Component is null.");

            if (!PrefabUtility.IsAddedComponentOverride(component))
                throw new ArgumentException("Cannot apply added component. Component is not an added component override on a Prefab instance.", nameof(component));

            ThrowExceptionIfInstanceIsPersistent(component);

            try
            {
                GameObject prefabSourceGameObject = GetCorrespondingObjectFromSourceAtPath(component.gameObject, assetPath);
                if (prefabSourceGameObject == null)
                    return;

                var originalComponentOrder = component.gameObject.GetComponents<Component>();

                var actionName = "Apply Added Component";
                if (action == InteractionMode.UserAction)
                {
                    string dependentComponents = string.Join(

View on GitHub (pinned to 225b0fbdb5)

Solutions

Null-check before calling: if (component == null) return;
Verify GetComponent returned a valid component before forwarding.
Use the Unity null check (component == null) which also catches destroyed UnityEngine.Object references.

Example fix

// before
var c = go.GetComponent<Rigidbody>();
PrefabUtility.ApplyAddedComponent(c, assetPath, InteractionMode.UserAction);

// after
var c = go.GetComponent<Rigidbody>();
if (c == null) return;
PrefabUtility.ApplyAddedComponent(c, assetPath, InteractionMode.UserAction);

Defensive patterns

Strategy: validation

Validate before calling

if (component == null) { Debug.LogWarning("Component is null; cannot apply."); return; }
PrefabUtility.ApplyAddedComponent(component, assetPath, action);

Type guard

static bool IsLiveComponent(Component c) => c != null && c.gameObject != null;

Prevention

Null-check (Unity null check) any Component before apply/revert APIs.
Re-resolve components via GetComponent immediately before the call.
Guard editor menu items against empty selections.

When it happens

Trigger: Calling ApplyAddedComponent(null, ...); passing a Component reference that was destroyed before the call; GetComponent<T>() returning null and being forwarded.

Common situations: Editor menu items that apply the currently selected component when nothing valid is selected; GetComponent lookups that silently return null; deferred apply operations whose target was destroyed.

Related errors

AI-assisted analysis of Unity-Technologies/UnityCsReference@225b0fbdb5 (2026-08-13). Data as JSON: /api/errors/dcf24d6ac2bccf5a. Report an issue: GitHub.