@Test(timeout = 5000)
public void testNull() throws Exception {

  final List<String> oneNull = new ArrayList<>(1); // empty data
  oneNull.add(null);
  final InputReader inputReader = generateInputReader(generateCompletableFuture(oneNull.iterator()));
  // Fetcher
  final ParentTaskDataFetcher fetcher = createFetcher(inputReader);
  // Should return 'null'
  assertEquals(null, fetcher.fetchDataElement());
}