title: [ERR_INVALID_ARG_TYPE]: The "path" argument must be of type string. Received type undefined, Mountebank
body: <p>npm start Giving me error whenever running mountebank server with ^2.0.0 version of mountebank </p>
  
  <pre><code>TypeError [ERR_INVALID_ARG_TYPE]: The "path" argument must be of type string. Received type undefined
      at validateString (internal/validators.js:125:11)
      at Object.join (path.js:1147:7)
      at loadCustomProtocols (./node_modules/mountebank/src/mountebank.js:102:25)
      at loadProtocols (./mountebank/node_modules/mountebank/src/mountebank.js:134:27)
      at Object.create (./mountebank/node_modules/mountebank/src/mountebank.js:169:21)
  </code></pre>
  
  <blockquote>
    <p>Index.js</p>
  </blockquote>
  
  <pre><code>const mb = require('mountebank')
  const settings = require('./settings');
  const helloService = require('./hello-service')
  
  const mbServerInstance =  mb.create({
          port: settings.ports,
          pidfile: '../mb.pid',
          logfile: '../mb.log',
          portofile: '../protofile.json',
          ipWhitelist: ['*']
      });
  
  
  mbServerInstance.then(function() {
      helloService.addService();
  });
  </code></pre>
  
  <p>Reference link : <a href="https://stackoverflow.com/questions/55698361/how-to-fix-the-path-argument-must-be-of-type-string-received-type-undefined">How to fix: &#39;The &quot;path&quot; argument must be of type string. Received type undefined&#39; when running &#39;vue add vuetify&#39;</a></p>
  
  <pre><code>npm uninstall -g @vue/cli
  npm install -g @vue/cli
  </code></pre>