Stats command not updated

[nus-pe-script]

Describe the bug Upon clearing the app and doing stats command, stats command shows nothing. Then undoing the previous clear, the stats command still show nothing even thought there is a book

To Reproduce Steps to reproduce the behavior:

1. Clear
2. stats
3. Undo
4. stats

Expected behavior Stats should have been updated.

Screenshots If applicable, add screenshots to help explain your problem.

Additional context Add any other context about the problem here.

OS and Java Version

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_{[original: dummy#43]}