docs: public boolean unregisterBlockListener(String handle) throws InvalidArgumentException {
  
          if (shutdown) {
              throw new InvalidArgumentException(format("Channel %s has been shutdown.", name));
          }
  
          checkHandle(BLOCK_LISTENER_TAG, handle);
          logger.trace(format("Unregister BlockListener with handle %s.", handle));
  
          LinkedHashMap<String, BL> lblockListeners = blockListeners;
          if (lblockListeners == null) {
              return false;
          }
  
          synchronized (lblockListeners) {
  
              return null != lblockListeners.remove(handle);
  
          }
      }