Verbatim from the docs, on read-csv: na_valuesscalar, str, list-like, or dict, default None Additional strings to recognize as NA/NaN. If dict passed,

Verbatim from the docs, on read-csv: na_valuesscalar, str, list-like, or dict, default None Additional strings to recognize as NA/NaN. If dict passed, specific per-column NA values. By default the following values are interpreted as NaN: ‘’, ‘#N/A’, ‘#N/A N/A’, ‘#NA’, ‘-1.#IND’, ‘-1.#QNAN’, ‘-NaN’, ‘-nan’, ‘1.#IND’, ‘1.#QNAN’, ‘<NA>’, ‘N/A’, ‘NA’, ‘NULL’, ‘NaN’, ‘n/a’, ‘nan’, ‘null’. You fix it by using `keep_default_na=False`, by the way.