named_scope lambda syntax

How would I pass an attribute name into a named_scope lambda?

I want to be able to search an active record class for nil values in a particular attribute. Would like to use a named_scope instead of find () because I want to tack other methods on the end of the result. Syntax I've tried:

# workouts table in mySQL: # attributes time, reps, weight, distance

class Workout < ActiveRecord::Base named_scope :no_score, lambda {|compare| {:conditions => ["? IS NULL", compare]}} # tried all these named_scope :no_score, lambda {|compare| {:conditions => {compare => nil }}} # forms of syntax named_scope :no_score, lambda {|compare| {:conditions => {compare.intern => nil }}} # with no success

WorkoutController @gym.workouts.no_score("time")

Any ideas where I"m going wrong with the syntax?

never mind, I sorted it out. Solution:

named_scope :no_score, lambda { |compare| { :conditions => "#{compare} IS NULL" }}