code: public void createSession(String sessionId) {
          boolean newSession = sessionId == null;
          sessionId = newSession ? newSessionId() : sessionId;
          SessionController controller = sessions.get(sessionId);
          
          if (controller == null) {
              controller = SessionController.create(sessionId, newSession);
              sessions.put(sessionId, controller);
          }
      }
docs: Creates a new session with the specified session id.
  
  @param sessionId The session id to associate with the new session.