Replace ClosedTransaction with NullTransaction

activerecord/lib/active_record/connection_adapters/abstract/transaction.rb

@@ -43,8 +43,8 @@ def savepoint_name
       end
     end
 
-    class ClosedTransaction < Transaction #:nodoc:
-      def initialize; super(nil); end
+    class NullTransaction < Transaction #:nodoc:
+      def initialize; end
       def closed?; true; end
       def open?; false; end
       def joinable?; false; end
@@ -203,14 +203,11 @@ def open_transactions
       end
 
       def current_transaction
-        @stack.last || closed_transaction
+        @stack.last || NULL_TRANSACTION
       end
 
       private
-
-        def closed_transaction
-          @closed_transaction ||= ClosedTransaction.new
-        end
+        NULL_TRANSACTION = NullTransaction.new
     end
   end
 end

activerecord/lib/active_record/connection_adapters/abstract_adapter.rb

@@ -46,7 +46,7 @@ module ConnectionAdapters # :nodoc:
 
     autoload_at 'active_record/connection_adapters/abstract/transaction' do
       autoload :TransactionManager
-      autoload :ClosedTransaction
+      autoload :NullTransaction
       autoload :RealTransaction
       autoload :SavepointTransaction
       autoload :TransactionState