Flutter ObjectDB cleanup during dispose

Well, I have a Cubit initialization in State<> class by value loaded from ObjectDB.

    @override
    void initState() {
        super.initState();
        final path = (Platform.isAndroid || Platform.isLinux) ? (Directory.current.path + '/theme.db') : '';
        final storage = path == '' ? IndexedDBStorage('theme') : FileSystemStorage(path);
        final db = SchemaDB<ColorThemeObjectdbSchema> (
            storage,
            (themeMap) => ColorThemeObjectdbSchema.fromMap(themeMap),
        );
        initTheme(db);
    }

And during disposing of the state I need to update data of database. This is my implementation

    @override
    void dispose() {
        db.cleanup();
        db.insert({'themeObject': defaultTheme});
        super.dispose();
    }

But I am getting these errors

Undefined name 'db' • lib/widgets/states/my_home_page_state.dart:72:3 • undefined_identifier

Undefined name 'db' • lib/widgets/states/my_home_page_state.dart:73:3 • undefined_identifier

The 72nd and 73rd lines are

        db.cleanup();
        db.insert({'themeObject': defaultTheme});

Thank you for help!