This is an unusual question but just in case you will need an answer. After researching and you find out that everything is good, you can basically say that you couldn't find anything wrong. Try to mix in humor if you can since this is an odd question. Also, take a moment to pretend to be thinking about the question before answering immediately.
The last sentence in the answer is a question you should say with a slight smile. That should lighten the tension a little and show that you are fully confident.
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