vaadin request wrapped session lose it's value

Hello everybody,

at the moment i’m trying to fix an Bug at the rights management. At the begin of the vaadin page the Wrapped Session has allways a value. When the admin press change user (to check the permission of it) rarely the getWrappedSession function returns null:

request.getWrappedSession().setAttribute("olduser", user); request.getWrappedSession().setAttribute("user", newuser); I allways call getWrappedSession at the start. So the variable should has an value.

Is this problem known?

I’m looking forward to help.