react render empty

according to react doc

Booleans, Null, and Undefined Are Ignored

false, null, undefined, and true are valid children. They simply don’t render. These JSX expressions will all render to the same thing:

https://reactjs.org/docs/jsx-in-depth.html#booleans-null-and-undefined-are-ignored

so

class x extends Component{
     render(){
       return(null);
    }
}