code: function handle(err, results) {
        if (err) {
          errors = errors || [];
          errors.push(err);
        }
        if (results) responses = responses.concat(results);
  
        // multi calls should ALWAYS return an array!
        if (!--calls) {
            callback(errors && errors.length ? errors.pop() : undefined, responses);
        }
      }
docs: handle multiple servers