title: How can I set yarn as the default packageManager for Angular CLI? I get "Cannot read property 'value' of null"
body: <p>When I run the below command </p>
  
  <pre><code>ng set --global packageManager=yarn
  </code></pre>
  
  <p>I get the below message </p>
  
  <pre><code>"get/set have been deprecated in favor of the config command"
  </code></pre>
  
  <p>and when I run ---</p>
  
  <pre><code> ng config cli.packageManager yarn
  </code></pre>
  
  <p>I get the below error message</p>
  
  <pre><code>Cannot read property 'value' of null
  TypeError: Cannot read property 'value' of null
  at ConfigCommand.set (C:\Users\Rahul\AppData\Roaming\npm\node_modules\@angular\cli\commands\config.js:207:36)
  at ConfigCommand.run (C:\Users\Rahul\AppData\Roaming\npm\node_modules\@angular\cli\commands\config.js:181:18)
  at C:\Users\Rahul\AppData\Roaming\npm\node_modules\@angular\cli\models\command-runner.js:278:30
  at Generator.next (&lt;anonymous&gt;)
  at fulfilled (C:\Users\Rahul\AppData\Roaming\npm\node_modules\@angular\cli\models\command-runner.js:4:58)
  at &lt;anonymous&gt;
  </code></pre>
  
  <p>How can I resolve this?</p>
  
  <p>Below is the version information
  I am using Java 8.</p>
  
  <pre><code>NPM version - 5.6.0
  Yarn version --1.7.0
  </code></pre>
  
  <p>ng - v  gives me the following result. I want to use Angular js</p>
  
  <pre><code>Angular CLI: 6.0.8
  Node: 8.11.3
  OS: win32 x64
  Angular:
  ...
  
  Package                      Version
  ------------------------------------------------------
  @angular-devkit/architect    0.6.8
  @angular-devkit/core         0.6.8
  @angular-devkit/schematics   0.6.8
  @schematics/angular          0.6.8
  @schematics/update           0.6.8
  rxjs                         6.2.1
  typescript                   2.7.2
  </code></pre>