docs: public String registerBlockListener(BlockListener listener) throws InvalidArgumentException {
  
          if (shutdown) {
              throw new InvalidArgumentException(format("Channel %s has been shutdown.", name));
          }
  
          if (null == listener) {
              throw new InvalidArgumentException("Listener parameter is null.");
          }
  
          String handle = new BL(listener).getHandle();
  
          logger.trace(format("Register event BlockEvent listener %s", handle));
  
          return handle;
  
      }