title: ERROR in Must have a source file to refactor
body: <p>Strange error with webpack compilation:</p>
  
  <blockquote>
    <p>ERROR in Must have a source file to refactor.</p>
  </blockquote>
  
  <p>Looking at the source code I found this message in <code>./node_modules/@ngtools/refactor.js</code>:</p>
  
  <pre><code>...   
  if (!sourceFile) {
    throw new Error('Must have a source file to refactor.');
  }
  </code></pre>
  
  <p>The configuration of @ngtools webpack plugin is pretty straightforward:</p>
  
  <pre><code>  {
      test: /\.ts$/,
      use: '@ngtools/webpack',
    } 
  </code></pre>