title: Karma: Error during loading "karma-phantomjs-launcher" plugin
body: <p>I am trying to run tests on Centos 7 within the Node.js (6.1.0) environment. After I run </p>
  
  <pre><code>./node_modules/karma/bin/karma --log-level debug start
  </code></pre>
  
  <p>I get the error message:</p>
  
  <pre><code>Error during loading "karma-phantomjs-launcher" plugin:
  Path must be a string. Received null
  </code></pre>
  
  <p>In karma.conf.js I have mentioned plugins and the browser:</p>
  
  <pre><code>'plugins': ['karma-mocha', 'karma-chai', 'karma-sinon', 'karma-chai-sinon', 'karma-coverage', 'karma-jasmine', 'karma-phantomjs-launcher', 'karma-chrome-launcher', 'karma-babel-preprocessor'],
  browsers: ['PhantomJS'],
  </code></pre>
  
  <p>I also have installed all plugins locally for the project. All other plugins are loaded without a problem.</p>
  
  <p>I have also the same project running on Windows 7 environment without a problem.</p>