Incorrect XLSX parsing

[AndrewKis]

pjTDYzyiTmEte21D_oIlIY6HL8t_5FH7f-Global Library Data.xlsx

After read has incorrect type in several columns - doesn't recognize empty cells as nulls but as String:

[Jolanrensen]

null is better than empty string indeed. That way we can use fillNulls {}.
Maybe we could streamline it with dataframe-csv. It uses ParserOptions with nullStrings containing "", "null", "NA" etc.