In this documentation, you tell:

UserSession userSession = WebEngine.getActiveContext().getUserSession();
Principal principal = userSession.getPrincipal();
CoreSession session1 = userSession.getCoreSession();
CoreSession session2 = userSession.getCoreSession("myrepo");    

does the right code is :

UserSession userSession = WebEngine.getActiveContext().getUserSession();
Principal principal = userSession.getPrincipal();
CoreSession session1 = WebEngine.getActiveContext().getCoreSession();
CoreSession session2 = WebEngine.getActiveContext().getCoreSession("myrepo");