def set(id, value, options = {})
      id = Array(id)
      id.push(nil) if id.empty?
      id[id.size - 1] ||= next_id(id[0..-2])
      with_redis do |redis|
        redis.set(redis_key_for(id), dump(value), redis_set_options.merge(options))
      end
      id.last
    end
def set(id, value, options = {})
      id = Array(id)
      id.push(nil) if id.empty?
      id[id.size - 1] ||= next_id(id[0..-2])
      with_redis do |redis|
        redis.set(redis_key_for(id), dump(value), redis_set_options.merge(options))
      end
      id.last
    end
Saves value to redis. If `id` is `nil`, it's generated with #next_id.
 Returns last part of id / generated id.