code: public static boolean register(@Nonnull Item item) {
          ItemDeletion instance = instance();
          if (instance == null) {
              return false;
          }
          instance.lock.writeLock().lock();
          try {
              return instance.registrations.add(item);
          } finally {
              instance.lock.writeLock().unlock();
          }
      }
docs: Register the supplied {@link Item} for deletion.
  
  @param item the {@link Item} that is to be deleted.
  @return {@code true} if and only if the {@link Item} was registered and the caller is now responsible to call
  {@link #deregister(Item)}.