title: flutter web error when try to build and existing flutter app
body: <p>I have an existing flutter app and try to run it on web but when I try to run 
  it shows a blank page and I saw an error on chrome console </p>
  
  <pre><code>Uncaught TypeError: Class extends value undefined is not a constructor or null
     at remote_module.dart:15
  </code></pre>