code: function getBundlesForArgument(arg)
  {
      // handles mix.bower(['package1', 'package2'])
      if (_.isArray(arg)) {
          return [new Bundle(arg)];
      }
  
      // handles mix.bower('namedBundle') where namedBundle is defined in bower.json
      if (_.isString(arg)) {
          return [new Bundle(BOWER_JSON.bundles[arg], arg)];
      }
  
      // handles mix.bower(), which uses all bundle definitions in bower.json
      if (BOWER_JSON.bundles && BOWER_JSON.bundles.length) {
          return _.map(BOWER_JSON.bundles || [], function (packages, name) {
              return new Bundle(packages, name);
          });
      }
  
      // handles mix.bower() when no "bundles" property, uses all from the
      // "dependencies" property as fallback
      if (BOWER_JSON.dependencies) {
          var packages = Object.keys(BOWER_JSON.dependencies);
          return [ new Bundle(packages) ];
      }
  
      return [];
  }
docs: Normalise argument given to mix.bower() to an array of Bundle objects.
  
  @param  {mixed} arg
  @return {array}