title: Path "/ngsw-config.json" already exists
body: <p>I have created a new angular project. Then I add</p>
  
  <p><code>ng add @angular/pwa</code> I got an error like this even I can't find the <em>ngsw-config.json</em> file</p>
  
  <blockquote>
    <p><strong>Path "/ngsw-config.json" already exist.</strong></p>
  </blockquote>
  
  <p>In angular CLI version is 6.1.1.</p>
  
  <blockquote>
    <p><strong>Invalid rule result: Function().</strong></p>
  </blockquote>
  
  <p>In angular CLI version is 6.0.3</p>