ActiveResource custom method #post broken

ActiveResource custom method #post doesn't work as described in docs.

class Person < ActiveResource::Base
 self.site = "http://37s.sunrise.i:3000"
end

Person.new(:name => 'Ryan).post(:register)  # POST /people/new/register.xml
# => { :id => 1, :name => 'Ryan' }

Due to a wrong check in method, it posts an empty string.