Hmmm... I think it is a YAML-related bug. I just checked it with a fully updated boot.properties. If I avoid the YAML-related code, the command works with the latest Java (11.0.2), Clojure (1.10.0) and Boot (2.8.2) versions...

Thanks a lot for your comments, @jayzawrotny!

Sure thing, glad I could help. In the long term it would be good to patch or file an issue with the affected yaml library. In the short term you could use Docker to build it against Java 8.

I've just opened a bug on this: https://github.com/hashobject/perun.io/issues/28