### Question:
MutableNullValueVector implements NullValueVectorReader { public MutableNullValueVector() { _nullBitmap = new ThreadSafeMutableRoaringBitmap(); } MutableNullValueVector(); void setNull(int docId); boolean isNull(int docId); @Override ImmutableRoaringBitmap getNullBitmap();  }### Answer:
@Test public void testMutableNullValueVector() { int[] docIds = new int[NUM_DOCS]; for (int i = 0; i < NUM_DOCS; i++) { int docId = RANDOM.nextInt(MAX_DOC_ID); _nullValueVector.setNull(docId); docIds[i] = docId; } for (int i = 0; i < NUM_DOCS; i++) { Assert.assertTrue(_nullValueVector.isNull(docIds[i])); } }