When the 7-day period of one of your bounties ends, you get the following message:
Your bounty on question [question title] is completed. You must award it to an answer within 24 hours.
However, in this case, there was no answer to award it to. In theory, it's possible somebody posts one in the 24 hour grace period, but wouldn't it better to not include the second sentence? Or perhaps rewrite the entire message as something like
Your bounty on question [question title] is completed but did not get an answer.
(Or perhaps even invite posting another bounty.)