switch present in favor of empty

activerecord/lib/active_record/nested_attributes.rb

@@ -386,7 +386,7 @@ def assign_nested_attributes_for_collection_association(association_name, attrib
         association.to_a
       else
         attribute_ids = attributes_collection.map {|a| a['id'] || a[:id] }.compact
-        attribute_ids.present? ? association.all(:conditions => {association.primary_key => attribute_ids}) : []
+        attribute_ids.empty? ? [] : association.all(:conditions => {association.primary_key => attribute_ids})
       end
 
       attributes_collection.each do |attributes|