If you receive the error Java::JavaLang::NullPointerExceptions when scheduling data deliveries to SFTP destinations, this may be due to a bug in JRuby that prevents the use of elliptic-curve (EC) algorithms and/or host keys for SSH connections from Looker to SFTP destinations.
To avoid issues with sending data to SFTP destinations, do not use EC algorithms in the ~/.ssh/config or /etc/ssh_config files or store EC host keys in ~/.ssh on your Looker host.