title: Error on Edit and Create: uncaught at handleFetch addRecords/newRecordsById
body: <p>I'm using <strong>admin-on-rest</strong>.</p>
  
  <p>When I press the <code>EditButton</code> in the List (no matter for what resource) I immediatly get the following error in the Firefox console:</p>
  
  <blockquote>
    <p>uncaught at handleFetch
    addRecords/newRecordsById&lt;@<a href="http://wzm-api.lcl:3000/static/js/bundle.js:45129:10" rel="nofollow noreferrer">http://wzm-api.lcl:3000/static/js/bundle.js:45129:10</a></p>
  </blockquote>
  
  <p>If i press the <code>SaveButton</code> the spinning indicator never ends.</p>
  
  <p>But the record is saved nevertheless.</p>
  
  <p>Do you have any idea what could be the problem?</p>