fails:Net::FTP#voidcmd sends the passed command to the server
fails:Net::FTP#voidcmd returns nil
fails:Net::FTP#voidcmd raises a Net::FTPReplyError when the response code is 1xx
fails:Net::FTP#voidcmd raises a Net::FTPReplyError when the response code is 3xx
fails:Net::FTP#voidcmd raises a Net::FTPTempError when the response code is 4xx
fails:Net::FTP#voidcmd raises a Net::FTPPermError when the response code is 5xx
fails:Net::FTP#voidcmd raises a Net::FTPProtoError when the response code is not valid
