fails:Net::FTP#nlst when switching type fails raises a Net::FTPPermError when the response code is 500
fails:Net::FTP#nlst when switching type fails raises a Net::FTPPermError when the response code is 501
fails:Net::FTP#nlst when switching type fails raises a Net::FTPPermError when the response code is 504
fails:Net::FTP#nlst when switching type fails raises a Net::FTPTempError when the response code is 421
fails:Net::FTP#nlst when switching type fails raises a Net::FTPPermError when the response code is 530
