public <R> R handleFirst(@NotNull CefBrowser browser, @NotNull HandlerCallable<T, R> callable) {
      List<T> list = get(browser);
      if (list == null) return null;
      for (T handler: list) {
        R result = callable.handle(handler);
        if (result != null) {
          return result;
        }
      }

      return null;
    }
public <R> R handleFirst(@NotNull CefBrowser browser, @NotNull HandlerCallable<T, R> callable)