def find_activity(activity_id)
      activity_hash = self.driver.find_activity(activity_id)
      if activity_hash
        # run hook
        self.run_hook(:did_find_activity, activity_hash)

        # unserialize
        Activr::Activity.from_hash(activity_hash)
      else
        nil
      end
    end
def find_activity(activity_id)
      activity_hash = self.driver.find_activity(activity_id)
      if activity_hash
        # run hook
        self.run_hook(:did_find_activity, activity_hash)

        # unserialize
        Activr::Activity.from_hash(activity_hash)
      else
        nil
      end
    end
Find an activity

 @param activity_id [Object] Activity id to find
 @return [Activity, Nil] An activity instance or `nil` if not found