/** * Used in forwardRef components to ensure ref exists * so that calling ref.current shall not throw error * * @example * * const Button = forwardRef((props, ref) => { * * // if ref exists, buttonRef = ref * // otherwise buttonRef is a newly created ref * const buttonRef = useEnsuredRef(ref); * * useEffect(() => { * // buttonRef will not be null even if ref is null * buttonRef.current.focus(); * }, []); * * return