apache/hadoop · error · NullPointerException

Key[] can not be null

Error message

Key[] can not be null

What it means

The array overload throws NullPointerException when the Key[] reference is null. The per-element loop then forwards each slot to addFalsePositive(Key), so a null element inside a non-null array trips the per-key check instead.

Source

Thrown at hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/util/bloom/RetouchedBloomFilter.java:186

   * @param keys The list of false positive.
   */
  public void addFalsePositive(List<Key> keys) {
    if (keys == null) {
      throw new NullPointerException("ArrayList<Key> can not be null");
    }

    for (Key k : keys) {
      addFalsePositive(k);
    }
  }

  /**
   * Adds an array of false positive information to <i>this</i> retouched Bloom filter.
   * @param keys The array of false positive.
   */
  public void addFalsePositive(Key[] keys) {
    if (keys == null) {
      throw new NullPointerException("Key[] can not be null");
    }

    for (int i = 0; i < keys.length; i++) {
      addFalsePositive(keys[i]);
    }
  }

  /**
   * Performs the selective clearing for a given key.
   * @param k The false positive key to remove from <i>this</i> retouched Bloom filter.
   * @param scheme The selective clearing scheme to apply.
   */
  public void selectiveClearing(Key k, short scheme) {
    if (k == null) {
      throw new NullPointerException("Key can not be null");
    }

    if (!membershipTest(k)) {

View on GitHub (pinned to 2add963021)

Solutions

  1. Pass new Key[0] when the array is absent
  2. Null-check the array reference before the call
  3. Allocate arrays eagerly while building the batch

Example fix

// before
rbf.addFalsePositive(keys); // keys may be null -> NPE

// after
rbf.addFalsePositive(keys != null ? keys : new Key[0]);
Defensive patterns

Strategy: validation

Validate before calling

rbf.addFalsePositive(keys != null ? keys : new Key[0]);

Prevention

When it happens

Trigger: rbf.addFalsePositive((Key[]) null); array accumulators that start as null and are only lazily allocated; varargs call sites passing an uninitialized array.

Common situations: Accumulator patterns that grow arrays on demand; fixed-size buffers reused across batches where null marks 'not built yet'.

Related errors

AI-assisted analysis of apache/hadoop@2add963021 (2026-08-22). Data as JSON: /api/errors/2d80d3e0997d9bd8. Report an issue: GitHub.