docs: public PutOperation<K, V> applyOperation(K key, PutOperation<K, V> existing, Operation<K, V> operation) {
      final Result<K, V> newValue = operation.apply(existing);
      if (newValue == null) {
        return null;
      } else {
        return newValue.asOperationExpiringAt(Long.MAX_VALUE);
      }
    }