title: Cannot read property 'map' of undefined in React
body: <p>I have the following component which is being called from a container component.  The container component passes the transactions prop.</p>
  
  <p>I know that the data property in prop is being passed in fine and has data and can be accessed from the console.log call.  However, when I try to map the data and create the list, I get an error: <code>Cannot read property 'map' of undefined</code></p>
  
  <p>Here is what the data looks like:</p>
  
  <pre><code>[
  {"transid":3426,"acct":"acct1","category":"Auto"},
   {"transid":3427,"acct":"acct2","category":"Subscriptions"}
  ]
  </code></pre>
  
  <p>What am I doing wrong?</p>
  
  <pre><code>import React from 'react';
  
  
  export default function TransactionManagerView (props) {
  
    console.log(props.data);
  
    return (
      &lt;ul&gt;
        {
          props.data.map(function(el,index) {
             return &lt;li key={index}&gt;{el.category}&lt;/li&gt;
          })
        }
      &lt;/ul&gt;
    )
  
  }
  </code></pre>