apache/beam · error · NullPointerException

input should not be null.

Error message

input should not be null.

What it means

The Histogram combiner's addInput method requires a non-null input element. Because the combiner accepts generic T values and casts them to Number, a null input would otherwise cause a less clear NullPointerException at the cast site, so an explicit NPE with the message 'input should not be null.' is thrown.

Solutions

1. Filter out null elements before the Histogram transform: apply(ParDo) or Filter.of(x -> x != null).
2. Replace nulls with a default value or NaN-handling strategy upstream.
3. Fix the source (e.g. set nullable=false in the schema) so nulls never enter the pipeline.

Example fix

// before
pcollection.apply(Histogram.globally(...));
// after
pcollection.apply(Filter.by(x -> x != null)).apply(Histogram.globally(...));

PCollection<T> nonNull = input.apply("DropNulls", Filter.by(v -> v != null));
nonNull.apply(Histogram.globally(...));

boolean isUsableInput(T v) { return v != null; }

try {
  histogramFn.addInput(accumulator, value);
} catch (NullPointerException e) {
  // skip or log the null element
}

When it happens

Trigger: Applying a Histogram combine/combineFn transform over a PCollection that contains null elements, or calling addInput(accumulator, null) directly on the combine function.

Common situations: Upstream parses/lookups returning null for missing values; Avro/JSON sources with missing fields producing null records; test pipelines feeding null as a sentinel.

Related errors

• bounds should be in ascending order without duplicates.
• cannot encode a null Integer
• cannot encode a null
• cannot encode a null String
• cannot encode a null ValueKind

AI-assisted analysis of apache/beam@12126d8942 (2026-09-13). Data as JSON: /api/errors/1376ed19e93e2cc3. Report an issue: GitHub.

Appendix: source

Thrown at sdks/java/extensions/combiners/src/main/java/org/apache/beam/sdk/extensions/combiners/Histogram.java:330

     * @param bucketBounds the instance of the {@link BucketBounds} class with desired parameters of
     *     the histogram.
     */
    public static <T extends Number> HistogramCombineFn<T> create(BucketBounds bucketBounds) {
      return new HistogramCombineFn<>(
          ArrayUtils.toPrimitive(bucketBounds.getBounds().toArray(new Double[0])),
          bucketBounds.getBoundsInclusivity());
    }

    @Override
    public HistogramAccumulator createAccumulator() {
      return new HistogramAccumulator(bounds.length + 1);
    }

    @Override
    public HistogramAccumulator addInput(HistogramAccumulator accumulator, T input)
        throws IllegalArgumentException {
      if (input == null) {
        throw new NullPointerException("input should not be null.");
      }

      Double inputDoubleValue = ((Number) input).doubleValue();
      if (inputDoubleValue.isNaN() || inputDoubleValue.isInfinite()) {
        throw new IllegalArgumentException("input should not be NaN or infinite.");
      }
      int index = Arrays.binarySearch(bounds, inputDoubleValue);
      if (index < 0) {
        accumulator.counts[-index - 1]++;
      } else {
        // This means the value is on bound, can be handled based on the bound inclusivity.
        if (boundsInclusivity == BoundsInclusivity.LOWER_BOUND_INCLUSIVE_UPPER_BOUND_EXCLUSIVE) {
          accumulator.counts[index + 1]++;
        } else {
          accumulator.counts[index]++;
        }
      }
      return accumulator;

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