C:\opt\jruby>jruby -S gem install rails
file:/C:/opt/jruby/lib/jruby.jar!/jruby/extract.rb:12:in `initialize': undefined
 method `getResource' for nil:NilClass (NoMethodError)
        from file:/C:/opt/jruby/lib/jruby.jar!/jruby/commands.rb:13:in `new'
        from file:/C:/opt/jruby/lib/jruby.jar!/jruby/commands.rb:13:in `gem'
        from C:/opt/jruby/bin/gem:1