Find Command Functionality Error

[nus-pe-script]

Describe the bug
The find command to find books based on keywords does not work for the books that are already in the system. The list command produces 5 books already in inventory, but find command doesn't work on them.

To Reproduce
Steps to reproduce the behavior:

1. Use list command - 5 books listed including Biology: A global approach
2. Do find biology
3. See error: 0 books listed!

Expected behavior
Expect to see the book biology: a global approach

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Reported by: @Meg1456
Severity: High

_{[original: nusCS2113-AY1819S1/pe-1#66]}