Fix. If any key-word argument is empty, set it to default.
Fix. If any key-word argument is empty, set it to default.

rfaulkner/wikipedia_user_metrics,wikimedia/analytics-user-metrics,wikimedia/analytics-user-metrics,rfaulkner/wikipedia_user_metrics,rfaulkner/wikipedia_user_metrics,wikimedia/user_metrics,wikimedia/user_metrics,wikimedia/user_metrics,wikimedia/analytics-user-metrics