public static <T extends Serializable> ItemImportResult<T> error(
      Exception exception, Long sizeInBytes) {
    Preconditions.checkNotNull(exception);
    return new ItemImportResult<>(null, sizeInBytes, Status.ERROR, exception);
  }
The size of the item we tried to import, successfully or not. Optional (nullable).
portability-spi-transfer/src/main/java/org/datatransferproject/spi/transfer/idempotentexecutor/ItemImportResult.java