TypeError: Cannot set property 'level' of null

test.js

var winston = require('winston');

winston.addColors({
	debug: 'cyan',
	event: 'magenta',
	fail: 'inverse'
});

var log = new winston.Logger({
	levels: {
		debug: 0,
		info: 1,
		warn: 2,
		error: 3,
		event: 4,
		fail: 5
	}
});

log.on('error', function(e) {
	console.log(e);
});

log.add(winston.transports.Console, {
	timestamp: true,
	colorize: true,
	level: 'debug'
});

log.add(winston.transports.Loggly, {
	level: 'error',
	subdomain: '<SUBDOMAIN>',
	auth: {
		username: '<USERNAME>',
		password: '<PASSWORD>'
	},
	inputName: '<INPUT-NAME>',
	inputToken: '<INPUT-TOKEN>',
	json: true
});

log.event('an event without metadata!');