CSV files can be completely empty: should trigger error (or only containing invisible characters) Files can only have a header, but no content ([example](https://github.com/open-numbers/ddf--gapminder--fasttrack/blob/7662c8447ac12f281849a9b67e44f89b77122eb1/ddf--datapoints--u5stunted_prc--by--country--time.csv)): should trigger warning
CSV files can be completely empty: should trigger error (or only containing invisible characters)
Files can only have a header, but no content (example): should trigger warning