apache/beam · error · CoderException

cannot encode a null BitSet

Error message

cannot encode a null BitSet

What it means

BitSetCoder.encode was handed a null BitSet. The coder serializes the BitSet's byte-length plus bytes and cannot represent absence; per Coder contract, null values must be handled by an outer NullableCoder. The null value argument is at fault, not the coder configuration.

Source

Thrown at sdks/java/core/src/main/java/org/apache/beam/sdk/coders/BitSetCoder.java:45

  private static final BitSetCoder INSTANCE = new BitSetCoder();
  private static final ByteArrayCoder BYTE_ARRAY_CODER = ByteArrayCoder.of();

  private BitSetCoder() {}

  public static BitSetCoder of() {
    return INSTANCE;
  }

  @Override
  public void encode(BitSet value, OutputStream outStream) throws CoderException, IOException {
    encode(value, outStream, Context.NESTED);
  }

  @Override
  public void encode(BitSet value, OutputStream outStream, Context context)
      throws CoderException, IOException {
    if (value == null) {
      throw new CoderException("cannot encode a null BitSet");
    }
    BYTE_ARRAY_CODER.encodeAndOwn(value.toByteArray(), outStream, context);
  }

  @Override
  public BitSet decode(InputStream inStream) throws CoderException, IOException {
    return decode(inStream, Context.NESTED);
  }

  @Override
  public BitSet decode(InputStream inStream, Context context) throws CoderException, IOException {
    return BitSet.valueOf(BYTE_ARRAY_CODER.decode(inStream, context));
  }

  @Override
  public void verifyDeterministic() throws NonDeterministicException {
    verifyDeterministic(
        this, "BitSetCoder requires its ByteArrayCoder to be deterministic.", BYTE_ARRAY_CODER);

View on GitHub (pinned to 12126d8942)

Solutions

1. Filter null BitSets from the PCollection with Filter.by(Objects::nonNull).
2. Use NullableCoder.of(BitSetCoder.of()) via setCoder() if nulls are valid.
3. Substitute an empty BitSet (new BitSet()) for null where semantically acceptable.
4. Null-check before calling encode() in custom code.

Example fix

// before
out.output(bitmap == null ? null : BitSet.valueOf(bitmap));
// after
out.output(bitmap == null ? new BitSet() : BitSet.valueOf(bitmap));

if (value == null) { throw new IllegalArgumentException("BitSet element is null; filter before encoding"); }

boolean isEncodable(BitSet v) { return v != null; }

try {
  coder.encode(value, out, Context.OUTER);
} catch (CoderException e) {
  LOG.error("Null BitSet element", e);
  throw e;
}

When it happens

Trigger: Encoding a null BitSet directly, or a PCollection<BitSet> containing null elements reaching serialization.

Common situations: Null BitSets returned from helper methods (e.g. building a bitset from a bitmap that was absent), aggregation results that are null, manual coder use in tests.

Related errors

• cannot encode a null Integer
• cannot encode a null Long
• cannot encode a null Short
• cannot encode a null byte[]
• cannot encode a null value

AI-assisted analysis of apache/beam@12126d8942 (2026-09-13). Data as JSON: /api/errors/22572159458e4a52. Report an issue: GitHub.