In my opinion, the helper should just accept what the model layer provides. Currently, it doesn't happen, but ideally the `SlmGoogleAnalytics\Analytics\Tracker#setPageUrl()` does check 1. is it a string and 2. is the string not empty and 3. is the string a valid URL.

This is something the model part of SlmGoogleAnalytics should define and for every flag. The script then can safely assume the page url is not set (null) or a valid one.

For now, all these checks are missing but I'd like to keep the helper renders as slim as possible (and not duplicating this logic).