Snowflake pandas pd_writer writes out tables with NULLs

Turns out, the documentation (arguably, Snowflake's weakest point) is out of sync with reality. This is the real issue: https://github.com/snowflakedb/snowflake-connector-python/issues/329. All it needs is a single character in the column name to be upper case and it works perfectly.

My workaround is to simply do: df.columns = map(str.upper, df.columns) before invoking to_sql.