Make sure we always pass a list to _get_column_lists (#4095)
Make sure we always pass a list to _get_column_lists (#4095)

(some data sources might return None as the columns list)
denisov-vlad/redash,getredash/redash,denisov-vlad/redash,alexanderlz/redash,alexanderlz/redash,denisov-vlad/redash,denisov-vlad/redash,getredash/redash,getredash/redash,alexanderlz/redash,denisov-vlad/redash,getredash/redash,alexanderlz/redash,getredash/redash