title: DS.AdapterError.extend fails
body: <p>based on documentation <a href="https://emberjs.com/api/data/classes/DS.AdapterError.html" rel="nofollow noreferrer">https://emberjs.com/api/data/classes/DS.AdapterError.html</a> I am trying to duplicate.</p>
  
  <p>my code : </p>
  
  <pre><code>  import DS from 'ember-data';
  
    export default DS.AdapterError.extend({ message: "Down for maintenance." });
  </code></pre>
  
  <p>but I just get errors</p>
  
  <pre><code>Uncaught TypeError: _emberData.default.AdapterError.extend is not a function
  </code></pre>
  
  <p>has anyone extended this error object? I ma truly just capturing 401,403 errors that happen during the ember-data transaction. I wanted to use some custom errors.</p>