output: #fixed code
                                @Override
    public void handleNewSession(String sessionId) {
      if (_zkClientForRoutingDataListener == null || _zkClientForRoutingDataListener.isClosed()) {
        return;
      }
      // Resubscribe
      _zkClientForRoutingDataListener.unsubscribeAll();
      _zkClientForRoutingDataListener.subscribeRoutingDataChanges(this, this);
      resetZkResources();
    }
input: #vulnerable code 
                                @Override
    public void handleNewSession(String sessionId) {
      if (_zkClientForListener == null || _zkClientForListener.isClosed()) {
        return;
      }
      // Resubscribe
      _zkClientForListener.unsubscribeAll();
      _zkClientForListener.subscribeRoutingDataChanges(this, this);
      resetZkResources();
    } 
                              #location 8 
                              #vulnerability type THREAD_SAFETY_VIOLATION