From Porcupine wiki

Administrators: How to migrate your applications from version 0.5 to 0.5.2

Upgrading to version 0.5.2 is pretty straightforward. Just apply the following changes:

1. The current session's user object is no longer accessed using HttpContext.current().session.user. Use HttpContext.current().user instead.
2. The porcupine.core.eventHandlers is renamed to porcupine.events. If your application uses event handlers update your imports accordingly. The methods of the event handlers' classes are now static methods instead of class methods (update the decorators accordingly and remove the first class argument).
3. Add the @db.transactional() decorator for all of your transactional web methods. This decorator must always be declared right after the main web method decorator (i.e. webmethods.remotemethod).