Uncaught TypeError: Cannot read property 'offsetHeight' of null at index.js:48 #12

requestAnimationFrame(function () {
 var stickyHeaderHeight = _this._fixed.offsetHeight;

import 'react-sticky-header/styles.css';
import StickyHeader from 'react-sticky-header';
class Header extends React.Component {
 state = {
 sticked: false,
 };
 changeSticked = isSticky => {
 this.setState({sticked: isSticky});
 }
 render() {
 const logo = require("../../images/logo_v2.svg");
 const logoSmall = require("../../images/logo_v1.svg");
 return (
 <StickyHeader
 // This is the sticky part of the header.
 onSticky={(sticky) => {
 this.changeSticked(sticky);
 }}
 header={
 <div className="header-root">
 <div className="mini-header__logo"><img className="main-logo" src={this.state.sticked ? logoSmall : logo} alt=""/>
 </div>
 <div className="mini-header__entry-switch">
 <ul className="header_menu t-primary-14 t-weight-b">
 <Link className="header-link" to="/about">About</Link>
 <Link className="header-link" to="/faq">FAQs</Link>
 <Link className="header-link" to="/contact">Contact us</Link>
 </ul>
 <Link className="mui-button" to="/registration">Sign Up</Link>
 </div>
 </div>
 }
 >
 <section>
 <p style={{height: '200px', backgroundColor: '#ff00ff'}}>
 This section will be what the sticky header scrolls over before entering into
 sticky state. See the gif above or run the test story book to see examples.
 </p>
 </section>
 </StickyHeader>
 )
 }
};
export default Header;