org.springframework.integration.ftp.session.FtpSession requires a path be passed to both the "list" and "listNames" methods. The path must have text.
The underlying Apache FTP client allows a file listing to be performed without a path (so it is performed in the default folder after logging in to the ftp server). The FTP protocol also does allow a "LIST" command to be performed without an explicit folder path.
I am currently integrating with two commercial FTP servers that require LIST to be performed without a folder path, but I can't achieve that with the current version of FTPSession.
I'm happy to make the code enhancement myself and perform a pull request. For reference I would change lines 66 to 75 to be: