Merb/Mongoid fix for ParseTree gem

gistfile1.rb

module Mongoid
  module Extensions
    module Object
      module Reflections
        extend ActiveSupport::Concern
          alias :invar :ivar
          undef :ivar
        def invar(name)
          if instance_variable_defined?("@#{name}")
            return instance_variable_get("@#{name}")
          end
          nil
        end
      end
    end
  end
end

module Mongoid
  module Relations
    module Accessors
      def relation_exists?(name)
        invar(name)
      end

      def substitute(name, object, options)
        set(name, invar(name).substitute(object, options))
      end
    end
  end
end