read_csv allow scalar arg to na_values #1944
Description
make it so na_values='abcdefg' is not interpreted as na_values=['a', 'b', 'c', 'd', 'e', 'f', 'g']
{{ message }}
make it so na_values='abcdefg' is not interpreted as na_values=['a', 'b', 'c', 'd', 'e', 'f', 'g']