Error during jenkins startup when trying to register_extension.

The error seen doing a jpi server:

Loading /Users/rteabeault/projects/rvm-plugin/models/rvm_wrapper.rb
ArgumentError: wrong number of arguments (2 for 1)
/Users/rteabeault/.rvm/gems/jruby-1.6.7.2/gems/jenkins-plugin-runtime-0.1.27/lib/jenkins/plugin.rb:116:in `register_extension'