TypeError: Cannot read property 'accessToken' of null

My React app is returning :
TypeError: Cannot read property ‘accessToken’ of null when tring to open the app without accessToken in the url

componentDidMount() {
    const currentComponent = this;
    const webAuth = new auth0.WebAuth({
      domain: 'xxx',
      clientID: 'xxx',
      audience: 'xxx',
      scope: 'openid profile'
    });
    webAuth.parseHash({ hash: window.location.hash }, (err, authResult) => {
      if (err) {
        return console.log("error");
      }
      else {
          webAuth.client.userInfo(authResult.accessToken, (err, user) => {
            if (user) {
              currentComponent.setState({
                authenticated: true
              })
            }
      })
}

why is authResult null?