"Error from DataBinding 'hiera' while looking up ': undefined method `empty?' for nil:NilClass on node" after switching from Apache/Passenger to puppetserver

After switching from Apache/Passenger to puppetserver I'm getting this error message when I do a puppet run:> Error from DataBinding 'hiera' while looking up 'custommodule::class::parameter': undefined method `empty?' for nil:NilClass on node server4711.mycompany.example.com Any ideas about that?