message: fix use-behavior bug
diff: @@ -19,7 +19,10 @@ export function useBehavior<T>(s: Behavior<T> | undefined): T | undefined {
  const [value, setValue] = useState(s?.value);
  useEffect(() => {
  - if (!s) return;
  + if (!s) {
  + if (value !== void 0) setValue(void 0);
  + return;
  + }
  let fst = true;
  const sub = s.subscribe((v) => {
  if (fst) {
  