Is it possible to return empty in react render function?

I have a notification component, and I have a timeout setting for it. After timeout I call this.setState({isTimeout:true}).

What I want to do is if already timeout, I want just render nothing:

render() {
  let finalClasses = "" + (this.state.classes || "");
  if (isTimeout){
    return (); // here has some syntax error
  }
  return (<div>{this.props.children}</div>);
}

The problem is:

return (); // here has some syntax error