apache/beam · error · CoderException

cannot encode a null SortedMap

Error message

cannot encode a null SortedMap

What it means

SortedMapCoder.encode() rejects null SortedMaps, mirroring MapCoder. Beam's wire format for maps has no null representation, so encoding null would corrupt the stream; the coder throws CoderException before writing anything. Use NullableCoder if nulls must be representable.

Solutions

1. Replace null with Collections.emptySortedMap() (or new TreeMap<>()) before encoding
2. Wrap with NullableCoder.of(sortedMapCoder) if nulls are legitimate values
3. Guard the DoFn/transform to skip or default null maps

Example fix

// before
out.add(null); // null TreeMap
// after
out.add(map == null ? Collections.emptySortedMap() : map);

if (map == null) { map = Collections.emptySortedMap(); }

boolean isEncodable(java.util.SortedMap<?,?> m) { return m != null; }

try { coder.encode(map, out, Context.OUTER); } catch (CoderException e) { /* handle null map */ }

When it happens

Trigger: Calling SortedMapCoder.of(kCoder, vCoder).encode(null, out, Context.OUTER), or a pipeline element producing a null TreeMap/SortedMap that gets encoded.

Common situations: DoFn emitting null for a missing sorted map; bean/record fields defaulting to null; deserialized objects with absent maps.

Related errors

• cannot encode a null Byte
• cannot encode a null Double
• cannot encode a null Float
• cannot encode a null Map
• cannot encode a null ReadableDuration

AI-assisted analysis of apache/beam@12126d8942 (2026-09-13). Data as JSON: /api/errors/633761c50d2dcb27. Report an issue: GitHub.

Appendix: source

Thrown at sdks/java/core/src/main/java/org/apache/beam/sdk/coders/SortedMapCoder.java:80

  private Coder<K> keyCoder;
  private Coder<V> valueCoder;

  private SortedMapCoder(Coder<K> keyCoder, Coder<V> valueCoder) {
    this.keyCoder = keyCoder;
    this.valueCoder = valueCoder;
  }

  @Override
  public void encode(SortedMap<K, V> map, OutputStream outStream)
      throws IOException, CoderException {
    encode(map, outStream, Context.NESTED);
  }

  @Override
  public void encode(SortedMap<K, V> map, OutputStream outStream, Context context)
      throws IOException, CoderException {
    if (map == null) {
      throw new CoderException("cannot encode a null SortedMap");
    }
    DataOutputStream dataOutStream = new DataOutputStream(outStream);

    int size = map.size();
    dataOutStream.writeInt(size);
    if (size == 0) {
      return;
    }

    // Since we handled size == 0 above, entry is guaranteed to exist before and after loop
    Iterator<Entry<K, V>> iterator = map.entrySet().iterator();
    Entry<K, V> entry = iterator.next();
    while (iterator.hasNext()) {
      keyCoder.encode(entry.getKey(), outStream);
      valueCoder.encode(entry.getValue(), outStream);
      entry = iterator.next();
    }

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