title: Grunt "watch" Warning: Path must be a string. Received undefined
body: <p>Grunt "Watch" doesn't want to proceed.</p>
  
  <p>Problem: 
  Running "watch" task
  Waiting...
  Warning: Path must be a string. Received undefined</p>
  
  <p>Here is the grunt watch in Gruntfile.js:</p>
  
  <pre><code>watch: {
    //Watch files for changes during "grunt serve"
    main: {
      options: {
          livereload: true,
          livereloadOnError: false,
          spawn: false
      },
      files: [createFolderGlobs(['*.js', '*.less','*.html','*.json']), '!src/bower_components/**/*.js', '!src/js/**/*.js', '!_SpecRunner.html','!.grunt'],
      tasks: [] //all the tasks are run dynamically during the watch event handler
  
    }
  },
  </code></pre>