This is the only part that worries me a bit but I wasn't able to test how Google handles `undefined`.
It if doesn't work we'll have to rewrite it as something like this:

```javascript
if (label) {
  $window.ga('send', category, action, label);
} else if (action) {
  $window.ga('send', category, action);
} else {
  $window.ga('send', category);
}
```