I'm using the puppetrun provider "customrun", but every run fails with this error message:

/var/log/foreman-proxy/proxy.log

D, [2015-08-25T18:06:15.559074 #27172] DEBUG -- : about to execute: ["/bin/true", "-ay -f -s", ["l2917022.sdst.sbaintern.de"]]
E, [2015-08-25T18:06:15.559362 #27172] ERROR -- : Exception 'no implicit conversion of Array into String' when executing '["/bin/true", "-ay -f -s", ["l2917022.sdst.sbaintern.de"]]'
E, [2015-08-25T18:06:15.561525 #27172] ERROR -- : Failed puppet run: Check Log files

My puppetrun configuration looks like this (i'm using /bin/true in this example just for demonstration purposes):

/etc/foreman-proxy/settings.d/puppet.yml

---
:enabled: true
:puppet_conf: /etc/puppet/puppet.conf
:puppet_url: https://l9994022.edst.ebaintern.de:8140
:puppet_ssl_ca: /var/lib/puppet/ssl/certs/ca.pem
:puppet_ssl_cert: /var/lib/puppet/ssl/certs/l9994022.edst.ebaintern.de.pem
:puppet_ssl_key: /var/lib/puppet/ssl/private_keys/l9994022.edst.ebaintern.de.pem
:puppet_provider: customrun
:customrun_cmd: /bin/true
:customrun_args: -ay -f -s