ProFTPd error during installation on fresh Ubuntu 16.04.3

I’m trying to install virtualmin 6.0.3 on a Digital Ocean Ubuntu 16.04.3 droplet using the --minimal flag. The installation proceeds until step 7 of phase 3, which is ProFTPd configuration. Installation halts after this error:


[7/17] Configuring ProFTPd █▒▒▒▒▒▒
Use of uninitialized value $hostname in concatenation (.) or string at /usr/share/perl5/Virtualmin/Config/Plugin/ProFTPd.pm line 80.
Use of uninitialized value $hostname in concatenation (.) or string at /usr/share/perl5/Virtualmin/Config/Plugin/ProFTPd.pm line 83.
Error: Failed to list systemd units :
Error

Failed to list systemd units :

▣▣▣ Cleaning up

[SUCCESS] Installation Complete!
[SUCCESS] If there were no errors above, Virtualmin should be ready
[SUCCESS] to configure at …

Any ideas, or anyone with a similar issue?