title: Run hyperledger fabric samples enroll admin error
body: <p>I try to run Hyperledger Fabric samples code from github(<a href="https://hyperledger-fabric.readthedocs.io/en/latest/write_first_app.html" rel="nofollow noreferrer">https://hyperledger-fabric.readthedocs.io/en/latest/write_first_app.html</a>).</p>
  
  <p>After I start Docker and run ./startFabric.sh, then I try to run node enrollAdmin.js to invoke a certificate signing request, but I got the following error:</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-html lang-html prettyprint-override"><code>➜  fabcar git:(2433afd) ✗ node enrollAdmin.js
   Store path:/Users/xiajun/.Trash/fabric-samples/fabcar/hfc-key-store
  Successfully enrolled admin user "admin"
  error: [Client.js]: Error: Missing parameter. Must have a username.
      at _setUserFromConfig (/Users/xiajun/.Trash/fabric-samples/fabcar/node_modules/fabric-client/lib/Client.js:1279:27)
      at Promise (/Users/xiajun/.Trash/fabric-samples/fabcar/node_modules/fabric-client/lib/Client.js:1431:11)
      at setUserContext (/Users/xiajun/.Trash/fabric-samples/fabcar/node_modules/fabric-client/lib/Client.js:1412:10)
      at promise.then.then.then.then (/Users/xiajun/.Trash/fabric-samples/fabcar/node_modules/fabric-client/lib/Client.js:1691:17)
  Error: Failed to load key or certificate and save to local stores.
      at promise.then.then.then.then.then.catch (/Users/xiajun/.Trash/fabric-samples/fabcar/node_modules/fabric-client/lib/Client.js:1701:19)
  Failed to enroll admin: Error: Failed to enroll admin</code></pre>
  </div>
  </div>
  </p>
  
  <p>I cannot find the answer from the Internet. Can Anyone help me?</p>