docs: private Data[] convertToData(T[] items) {
          if (items == null || items.length == 0) {
              return new Data[0];
          }
          if (items[0] instanceof Data) {
              return (Data[]) items;
          }
          final Data[] ret = new Data[items.length];
          for (int i = 0; i < items.length; i++) {
              ret[i] = convertToData(items[i]);
          }
          return ret;
      }