Add a test for N/A key rejection. (#138)
Fix a bug that N/A values are accepted as keys. (#138)
Fix a typo.
Add a test for Column::contains(). (#135)
Add Index::num_entries(). (#135)
Update Column::contains() to use Index::num_entries(). (#135)
Add a test for Column::find_one(). (#135)
Fix a bug that an indexes column cannot find N/A with find_one(). (#135)