Grunt watch pattern.indexOf is not a function
<p>I'm trying to use Grunt's grunt-contrib-watch plugin to watch some files and then run the tasks, just what it was made for, this is my <strong>Gruntfile.js</strong></p>

<pre><code>module.exports = function(grunt){
    grunt.initConfig({
        pkg: grunt.file.readJSON('package.json'),
        sass: {
            options: {
                sourceMap: true,
                outputStyle: 'compressed'
            },
            dist: {
                files: {
                    'static/stylesheets/main.min.css': 'static/stylesheets/sass/main.scss',
                    /*'bower_components/foundation-sites/dist/foundation.min.css': 'bower_components/foundation-sites/scss/foundation.scss'*/
                }
            }
        },
        uglify: {
            dist: {
                files: {
                    'static/javascript/main.min.js': 'static/javascript/main.js'
                }
            }
        },
        watch: {
            files: [
                '&lt;%= sass.dist.files %&gt;',
                '&lt;%= uglify.dist.files %&gt;'
            ],
            tasks: [
                'sass',
                'uglify'
            ]
        }
    });

    grunt.loadNpmTasks('grunt-contrib-watch');
    grunt.loadNpmTasks('grunt-sass');
    grunt.loadNpmTasks('grunt-contrib-uglify');

    grunt.registerTask('default', ['watch']);
};
</code></pre>

<p>When I run it, it runs over and over and over again, and when I stop it, I see I have  this message:</p>

<blockquote>
  <p>Running "watch" task 
  Waiting... 
  Warning: pattern.indexOf is not a function</p>
</blockquote>

<p>I really don't know what's the problem. Does anybody know what happens here?</p>

<p><strong>UPDATE:</strong></p>

<p>Apparently, the problem is because of the way I call the files, because I changed it to: 'static/stylesheets/sass/*.scss' and it worked well, but I would like to know why the other way doesn't work, because I think is a more useful way to do it.</p>