title: NameSpace Issue in JointJS version 3
body: <p>I am trying to convert a legacy app from JointJS v2.2.1 to v3.0.2.  I’m hitting an error others have found:</p>
  
  <blockquote>
    <p>Uncaught Error: dia.ElementView: markup required. (joint.min.js:8)</p>
  </blockquote>
  
  <p>A helpful person said: “Please note you need to be careful with the cellViewNamespace for the dia.Paper and cellNamespace option for the dia.Graph in this setup.  Running this snippet is a quick check you've set up the namespaces correctly:</p>
  
  <pre><code>const cells = JSON.stringify(graph.toJSON());
  graph.clear();
  graph.fromJSON(JSON.parse(cells));
  </code></pre>
  
  <p>”</p>
  
  <p>Can anyone offer additional help?  I don’t know enough about JointJS to resolve this issue and I don’t really understand the code snippet.</p>