private static void UpdateCleanup()
        {
            AssetDatabase.ImportAsset(AGXUnityDirectory,
                                      ImportAssetOptions.ImportRecursive |
                                      ImportAssetOptions.DontDownloadFromCacheServer |
                                      ImportAssetOptions.ForceSynchronousImport);
#if UNITY_2020_1_OR_NEWER
            EditorApplication.update += OnEditorUpdate;
            DefineSymbols.Add(OnImportDefineSymbol);
#endif
        }