def preferred?(name, group = nil)
      name = name.to_s
      assert_valid_preference(name)
      
      value = preferred(name, group)
      preference_definitions[name].query(value)
    end
def preferred?(name, group = nil)
      name = name.to_s
      assert_valid_preference(name)
      
      value = preferred(name, group)
      preference_definitions[name].query(value)
    end
Queries whether or not a value is present for the given preference.
 This is dependent on how the value is type-casted.

 == Examples

   class User < ActiveRecord::Base
     preference :color, :string, :default => 'red'
   end

   user = User.create
   user.preferred(:color)              # => "red"
   user.preferred?(:color)             # => true
   user.preferred?(:color, 'cars')     # => true
   user.preferred?(:color, Car.first)  # => true

   user.write_preference(:color, nil)
   user.preferred(:color)              # => nil
   user.preferred?(:color)             # => false