Rails - Jul 2006 - composed_of and validates_presence_of

I''m using composed_of in one of my models, and I''d like to
validate
that the attribute is present.

class Hand < AR::Base
  composed_of :level, :mapping => [ %w(sb sb), %w(bb bb), %w(ante ante) ]
  validates_presence_of :level, :message => "must be set"
end

The Level class itself is very simple:

class Level
  include Reloadable
  attr_reader :sb, :bb, :ante

  def initialize(sb, bb, ante)
    @sb, @bb, @ante = sb.to_i, bb.to_i, ante.to_i
    raise "SB can''t be 0" unless @sb > 0
    raise "BB can''t be 0" unless @bb > 0
    raise "SB can''t be bigger than BB" if @sb > @bb
    raise "Ante can''t be bigger than SB" if @ante > @sb
  end
end

The problem is that if  create a new hand and don''t set the level
object, calling valid? results in the level object being created with
null values.  null gets turned into 0 which raises an error.

The behavior I want is to simply have valid? return false, saying that
the reason is that level is null.  Can I do that?

Pat