public void enter() {
        LinkedList<ScopeState> stack = values.get();
        if (stack == null) {
            stack = new LinkedList<>();
            values.set(stack);
        }
        stack.addFirst(new ScopeState());
    }

    private ScopeState getScopeState() {
        LinkedList<ScopeState> stack = values.get();
        if (stack == null || stack.isEmpty()) {
            throw new IllegalStateException();