code: function getMapOption(from) {
          if (typeof options.map === 'string') {
              var mapPath = options.map + path.basename(from) + '.map';
  
              if (grunt.file.exists(mapPath)) {
                  return grunt.file.read(mapPath);
              }
          }
  
          return options.map;
      }
docs: Returns an input source map if a map path was specified
  or options.map value otherwise
  @param {string} from
  @returns {string|boolean|undefined}