code: public String clearSession() {
  
          synchronized (sharedLock) {
              SessionData session = loadSession();
              String id = session != null ? session.getSessionId() : null;
              clearAll();
              sharedLock.notifyAll();
              return id;
          }
      }
docs: Deletes currently saved session.
  
  @return SessionId for the deleted session or null if no session was active.