This week's book giveaway is in the Agile and Other Processes forum. We're giving away four copies of Real-World Software Development: A Project-Driven Guide to Fundamentals in Java and have Dr. Raoul-Gabriel Urma & Richard Warburton on-line! See this thread for details.
There isn't any exception stack trace there. That Log message is just at the info level, not an error. All it is saying is that there is an object in the collection that has no id set, so therefore no record in the database to delete.