docs: @Deprecated
      public void addWatcher(Listener watcher) {
          if (watcher == null) {
              throw new IllegalArgumentException("Null watcher added");
          }
  
          synchronized (mutex) {
              if (watcherExecutor.isShutdown()) {
                  throw new IllegalStateException("Adding watcher on closed FileWatcher");
              }
              watchers.add(() -> watcher);
          }
      }