Ruby croaks on composition

gistfile1.rb

class Record < Sequel::Model
  many_to_one :domain
  plugin :validation_helpers, :composition
                                                                     
  composition :serial,
    :composer => proc { split(content) if type == 'SOA' },
    :decomposer => (
      proc do

....


$ ramaze console
Middlewares for spec
I [2012-03-30 23:37:15 $31139]  INFO | : Environment not set; using dev mode
I [2012-03-30 23:37:15 $31139]  INFO | : We start in dev mode
/home/leucos/dev/sysadmin/pdnsui/model/record.rb:5:in `<class:Record>': undefined method `composition' for Record:Class (NoMethodError)
	from /home/leucos/dev/sysadmin/pdnsui/model/record.rb:1:in `<top (required)>'