to support what I suggest in comment, we can do it like this here:
```javascript
_.each(transports, function(options, type) {
  if ('undefined' === winston.transports[type]) {
    grunt.log.error('Cannot instantiate non-default transport: ' + transport.clazz);
  } else {
    logger.add(winston.transports[type], options);
  }
});
```