code: public final void addChainEventListener(ChainEventListener listener) {
          if (TraceComponent.isAnyTracingEnabled() && tc.isDebugEnabled()) {
              Tr.debug(this, tc, "addChainEventListener: " + listener);
          }
          if (null != listener) {
              this.chainEventListeners.add(listener);
          }
      }
docs: Enables external entities to be notified of chain events described in
  ChainEventListener interface.
  
  @param listener