title: TypeError: Unable to get property 'map' of undefined or null reference
body: <p>This (<a href="https://github.com/sanity-io/example-frontend-next-js" rel="nofollow noreferrer">https://github.com/sanity-io/example-frontend-next-js</a>) react example works well when I run. But integrating with an existing react (reducer-redux) app. I am getting
  <code>TypeError: Unable to get property 'map' of undefined or null reference</code></p>
  
  <p>I think the problem comes from my ReactDOM.render() according to the stack trace on chrome. Any help, please?</p>