code: function (next) {
  
          async.each(input, function (path, done) {
              fs.stat(path, function (err, stats) {
                  if (err) return done(err);
                  if (stats.isDirectory())
                      return done("Cannot have a directory as input");
                  done();
              });
          }, next);
  
      }
docs: make sure no directories in the input list