docs: public void addMessageListener(JMessageListener listener)
      {
          if (listener == null)
              return; // Never
          this.removeDuplicateFilters(listener);  // Remove any duplicate record filters
          if (m_vListenerList == null)
              m_vListenerList = new Vector<JMessageListener>();
          for (int i = 0; i < m_vListenerList.size(); i++)
          {
              if (m_vListenerList.get(i) == listener)
              {
                  Util.getLogger().warning("--------Error-Added message listener twice--------");
                  return;     // I'm sure you didn't mean to do that.
              }
          }
          m_vListenerList.add(listener);
          listener.addListenerMessageFilter(this);
      }