Can't run jruby commands on Logstash 8

Elastic Stack Logstash
1

Hi,
We're looking to upgrade our ELK stack from 7.17 to 8.16 however I've discovered an issue with the jruby command throwing an error on 8.16 which means we can't build and install logstash plugins.

e.g.

# /usr/share/logstash/vendor/jruby/bin/jruby
Error: No such file or directory: 
/usr/share/logstash/vendor/jruby/bin/jruby: line 729: exec: : not found

While it behaves as expected on logstash 7.17.

I notice the breaking changes mention removing the Ruby execution engine, is this related?

If I compare The shell on V.8:

if $use_exec; then
    exec "$@"
else
    "$@"

With V7:

if $use_exec; then
  exec "${jvm_command[@]}"
else
  "${jvm_command[@]}"

Again, does this need tweaked on V8? Note this is a fresh install of logstash on a brand new Dev VM- I haven't configured any external JDKs or config.