jruby java objects to_json with Gson

gson_builder.rb

require 'gson-1.6.jar'
class GsonBuilder

   include_package "com.google.gson"

  def initialize
     @gson = GsonBuilder.new.setFieldNamingPolicy(FieldNamingPolicy::LOWER_CASE_WITH_UNDERSCORES).serializeNulls().create()
  end

  def to_json(obj)
    @gson.to_json(obj)
  end

end


gson = Gson.new 
obj = someJavaObject.new
p gson.to_json(obj)

seems to have a bug, should be "class Gson" instead of GsonBuilder.