code: @SuppressWarnings("unchecked")
      public static <T> AttachmentKey<AttachmentList<T>> createList(final Class<? super T> valueClass) {
          return new ListAttachmentKey(valueClass);
      }
docs: Construct a new list attachment key.
  
  @param valueClass the list value class
  @param <T>        the list value type
  @return the new instance