Unity-Technologies/UnityCsReference · error · ArgumentNullException

guid

Error message

guid

What it means

PrefabFamilyPopup.GetPrefabAssetIdentifier computes a Hash128 from a GUID string to use as a cache key for prefab asset info. The method throws ArgumentNullException when the guid parameter is null or empty, since Hash128.Compute on an empty string would produce a meaningless key. This is a precondition guard on an internal static utility method.

Source

Thrown at Editor/Mono/Prefabs/PrefabFamilyPopup.cs:634

        }

        public static PrefabAssetInfo GetState(string guid)
        {
            var id = GetPrefabAssetIdentifier(guid);
            var cachedPrefabAssetInfo = s_StateCache.GetState(id);
            if (cachedPrefabAssetInfo == null)
                return null; // not cached yet

            var currentPrefabSourceFileHash = AssetDatabase.GetSourceAssetFileHash(guid);
            if (currentPrefabSourceFileHash != cachedPrefabAssetInfo.prefabFileHash)
                return null; // cache is out of sync

            return cachedPrefabAssetInfo;
        }
        public static Hash128 GetPrefabAssetIdentifier(string guid)
        {
            if (string.IsNullOrEmpty(guid))
                throw new ArgumentNullException(nameof(guid));

            return Hash128.Compute(guid);
        }
    }

    class OverridesCounterForPrefabAssets
    {
        GameObject[] m_PrefabAssetRoots;
        List<int> m_OverridesCount;
        int m_CurrentAssetIndex;
        int m_CurrentStep;
        bool m_ChangedCount;

        bool m_Debug = false;

        public OverridesCounterForPrefabAssets(GameObject[] prefabInstanceRoots)
        {
            m_PrefabAssetRoots = prefabInstanceRoots;

View on GitHub (pinned to 225b0fbdb5)

Solutions

1. Check string.IsNullOrEmpty(guid) before calling GetPrefabAssetIdentifier
2. Verify the source GameObject is an asset (PrefabUtility.IsPartOfPrefabAsset) before extracting its GUID
3. Use AssetDatabase.TryGetAssetPathFromGUID or validate the GUID format before passing it

Example fix

// before
Hash128 id = PrefabFamilyPopup.GetPrefabAssetIdentifier(guid);

// after
if (!string.IsNullOrEmpty(guid))
    Hash128 id = PrefabFamilyPopup.GetPrefabAssetIdentifier(guid);
else
    return; // or handle the missing-asset case

if (string.IsNullOrEmpty(guid))
    throw new InvalidOperationException("GUID is null or empty — cannot compute prefab asset identifier.");
// Safe to call GetPrefabAssetIdentifier(guid)

static bool IsValidGuid(string guid) => !string.IsNullOrEmpty(guid) && guid.Length == 32;

try { Hash128 id = PrefabFamilyPopup.GetPrefabAssetIdentifier(guid); }
catch (ArgumentNullException ex) when (ex.ParamName == "guid")
{ Debug.LogError("GUID is null or empty."); }

When it happens

Trigger: Calling PrefabFamilyPopup.GetPrefabAssetIdentifier(null) or GetPrefabAssetIdentifier("") directly. Passing a GUID obtained from AssetDatabase.AssetPathToGUID on a path that returned an empty string (e.g., for a scene object that is not an asset).

Common situations: Code that derives a GUID from an asset path but doesn't check whether the path resolved to a valid asset. Scene objects passed to asset-guid lookup functions. Programmatically constructed objects that have no asset backing.

Related errors

• prefabInstance
• The inputObject is null
• Provided GameObject is not a Prefab instance
• Given input object is not a prefab asset
• Object to create variant from has to be a Prefab root

AI-assisted analysis of Unity-Technologies/UnityCsReference@225b0fbdb5 (2026-08-13). Data as JSON: /api/errors/1c81de539a51ab18. Report an issue: GitHub.