title: TypeError: unhashable type: 'dict', when dict used as a key for another dict
body: <p>I have this piece of code:</p>
  
  <pre><code>for element in json[referenceElement].keys():
  </code></pre>
  
  <p>When I run that code, I get this error:</p>
  
  <blockquote>
    <p>TypeError: unhashable type: 'dict'</p>
  </blockquote>
  
  <p>What is the cause of that error and what can I do to fix it?</p>