code: public synchronized void connectionClosed (Connection conn)
      {
          // remove the session from the connection map
          PresentsSession session = _conmap.remove(conn);
          if (session != null) {
              log.debug("Unmapped session", "session", session, "conn", conn);
              // let the session know the connection went away
              session.wasUnmapped();
  
          } else {
              log.debug("Closed unmapped connection '" + conn + "'. " +
                      "Session probably not yet authenticated.");
          }
      }
docs: Called by the connection manager to let us know when a connection has been closed.