when 'db' keyword arg is not specified in object construction the connection is set to None
when 'db' keyword arg is not specified in object construction the connection is set to None

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