MockControl mockRequest = MockControl.createControl(PortletRequest.class);
PortletRequest request = (PortletRequest) mockRequest.getMock();
request.getPortletSession(false); // must not create Session for null value...
mockRequest.setReturnValue(session);
session.removeAttribute("foo", PortletSession.APPLICATION_SCOPE);
mockSession.setVoidCallable();
mockRequest.replay();
mockSession.replay();
PortletUtils.setSessionAttribute(request, "foo", null, PortletSession.APPLICATION_SCOPE);