Use backwards-compatible size instead of length to check association proxy.

Author: aepstein

lib/declarative_authorization/authorization.rb

@@ -513,7 +513,7 @@ def validate? (attr_validator, object = nil, hash = nil)
       return false unless object
 
       if Authorization.is_a_association_proxy?(object)
-        return false unless object.length > 0
+        return false if object.empty?
         object.each do |member|
           return true if validate?(attr_validator, member, hash)
         end