public boolean isNull(int docId) {
    return getNullBitmap().contains(docId);
  }
@Test
  public void testNullValueVectorReader()
      throws IOException {
    Assert.assertEquals(TEMP_DIR.list().length, 1);
    File nullValueFile = new File(TEMP_DIR, TEMP_DIR.list()[0]);
    PinotDataBuffer buffer = PinotDataBuffer.loadBigEndianFile(nullValueFile);
    NullValueVectorReader reader = new NullValueVectorReaderImpl(buffer);
    for (int i = 0; i < 100; i++) {
      Assert.assertTrue(reader.isNull(i));
    }
  }