title: Map on an initial undefined value
body: <p>Is there anything in REACT like in Angular where you can make a nullable type? In angular you would do something like crawlList?.jobsList</p>
  
  <pre><code>{crawlList.jobsList.map(crawl =&gt; (
     &lt;div&gt;test&lt;/div&gt;
  ))}
  </code></pre>
  
  <p>The challenge is I set jobsList dynamically on a click, but on initial load above will fail with "Cannot read property 'map' of undefined". Or du you need to initialize the data?</p>