# ADR-0008 - Use NullAway for null checking

## Date

2025-08-06

## Context

Our codebase uses `null` extensively to represent an absence of value or optionality of the argument.
We utilize nullness annotations in Java code and somewhat rely on IDE warnings to guide us.
However, the Java code we have is not fully annotated, which causes several consequences:
* IDE warnings can be misleading

    nextInBucketVToK[src] = ABSENT;
  }

  @Override
  public void clear() {
    Arrays.fill(keys, 0, size, null);
    Arrays.fill(values, 0, size, null);
    Arrays.fill(hashTableKToV, ABSENT);
    Arrays.fill(hashTableVToK, ABSENT);
    Arrays.fill(nextInBucketKToV, 0, size, ABSENT);
    Arrays.fill(nextInBucketVToK, 0, size, ABSENT);
    Arrays.fill(prevInInsertionOrder, 0, size, ABSENT);

  }

  @CollectionSize.Require(absent = ZERO)
  @MapFeature.Require(ALLOWS_NULL_VALUES)
  public void testContainsEntryWithNullValuePresent() {
    initMapWithNullValue();
    assertTrue(getMap().entrySet().contains(mapEntry(getKeyForNullValue(), null)));
  }

  @MapFeature.Require(SUPPORTS_PUT)
  @CollectionSize.Require(absent = ZERO)
  public void testSetValue() {

  }

  @CollectionSize.Require(absent = ZERO)
  @MapFeature.Require(ALLOWS_NULL_VALUES)
  public void testContainsEntryWithNullValuePresent() {
    initMapWithNullValue();
    assertTrue(getMap().entrySet().contains(mapEntry(getKeyForNullValue(), null)));
  }

  @MapFeature.Require(SUPPORTS_PUT)
  @CollectionSize.Require(absent = ZERO)
  public void testSetValue() {

    assertWithMessage(rootLocaleFormat("%s must be inherited.", annotationClass))
        .that(annotationClass.getAnnotation(Inherited.class))
        .isNotNull();

    for (String propertyName : new String[] {"value", "absent"}) {
      Method method = null;
      try {
        method = annotationClass.getMethod(propertyName);
      } catch (NoSuchMethodException e) {
        throw new AssertionError("Annotation is missing required method", e);

48(CX), X0 AESENC X0, X1 AESENC X0, X2 AESENC X0, X3 AESENC X0, X4 AESENC X0, X5 AESENC X0, X6 AESENC X0, X7 AESENC X0, X8 MOVUPS 64(CX), X0 AESENC X0, X1 AESENC X0, X2 AESENC X0, X3 AESENC X0, X4 AESENC X0, X5 AESENC X0, X6 AESENC X0, X7 AESENC X0, X8 MOVUPS 80(CX), X0 AESENC X0, X1 AESENC X0, X2 AESENC X0, X3 AESENC X0, X4 AESENC X0, X5 AESENC X0, X6 AESENC X0, X7 AESENC X0, X8 MOVUPS 96(CX), X0 AESENC X0, X1 AESENC X0, X2 AESENC X0, X3 AESENC X0, X4 AESENC X0, X5 AESENC X0, X6 AESENC X0, X7 AESENC...

    // count == 1
    segment.count++;
    assertSame(value, segment.get(key, hash));
    assertTrue(segment.containsKey(key, hash));
    assertTrue(segment.containsValue(value));
    // don't see absent values now that count > 0
    assertThat(segment.get(new Object(), hash)).isNull();

    // null key
    InternalEntry<Object, Object, ?> nullEntry = segment.newEntryForTesting(null, hash, entry);

    // count == 1
    segment.count++;
    assertSame(value, segment.get(key, hash));
    assertTrue(segment.containsKey(key, hash));
    assertTrue(segment.containsValue(value));
    // don't see absent values now that count > 0
    assertThat(segment.get(new Object(), hash)).isNull();

    // null key
    InternalEntry<Object, Object, ?> nullEntry = segment.newEntryForTesting(null, hash, entry);

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    segment.count++;
    assertThat(segment.get(key, hash)).isSameInstanceAs(value);
    assertThat(segment.containsKey(key, hash)).isTrue();
    assertThat(segment.containsValue(value)).isTrue();
    // don't see absent values now that count > 0
    assertThat(segment.get(new Object(), hash)).isNull();

    // null key
    DummyEntry<Object, Object> nullEntry = DummyEntry.create(null, hash, entry);