apache/beam · error · IllegalArgumentException

Unexpected type ${fieldType}

Error message

Unexpected type ${fieldType}

What it means

This is the terminal default branch of AvroUtils.getFieldSchema: the Beam FieldType's TypeName has no case in the Beam->Avro conversion switch, so the converter throws IllegalArgumentException naming the unexpected type. It is a guard against future/unhandled FieldType variants being silently mis-converted.

Source

Thrown at sdks/java/extensions/avro/src/main/java/org/apache/beam/sdk/extensions/avro/schemas/utils/AvroUtils.java:1264

        break;

      case MAP:
        if (checkNotNull(fieldType.getMapKeyType()).getTypeName().isStringType()) {
          // Avro only supports string keys in maps.
          baseType =
              org.apache.avro.Schema.createMap(
                  getFieldSchema(checkNotNull(fieldType.getMapValueType()), fieldName, namespace));
        } else {
          throw new IllegalArgumentException("Avro only supports maps with string keys");
        }
        break;

      case ROW:
        baseType = toAvroSchema(checkNotNull(fieldType.getRowSchema()), fieldName, namespace);
        break;

      default:
        throw new IllegalArgumentException("Unexpected type " + fieldType);
    }
    return fieldType.getNullable() ? ReflectData.makeNullable(baseType) : baseType;
  }

  private static final Map<org.apache.avro.Schema, Function<Number, ? extends Number>>
      NUMERIC_CONVERTERS =
          ImmutableMap.of(
              org.apache.avro.Schema.create(org.apache.avro.Schema.Type.INT), Number::intValue,
              org.apache.avro.Schema.create(org.apache.avro.Schema.Type.LONG), Number::longValue,
              org.apache.avro.Schema.create(org.apache.avro.Schema.Type.FLOAT), Number::floatValue,
              org.apache.avro.Schema.create(org.apache.avro.Schema.Type.DOUBLE),
                  Number::doubleValue);

  /** Convert a value from Beam Row to a vlue used for Avro GenericRecord. */
  private static @Nullable Object genericFromBeamField(
      FieldType fieldType, org.apache.avro.Schema avroSchema, @Nullable Object value) {
    TypeWithNullability typeWithNullability = new TypeWithNullability(avroSchema);
    if (fieldType.getNullable() != typeWithNullability.nullable) {

View on GitHub (pinned to 12126d8942)

Solutions

1. Map the field to a supported Beam TypeName (primitive, ARRAY, ITERABLE, MAP, ROW) before Avro conversion.
2. Upgrade the Beam Avro extension / Beam SDK so the type has a mapping.
3. Convert the field manually to its Avro Schema and bypass toAvroSchema for that column.
4. Catch IllegalArgumentException and skip/serialize the offending field with a custom encoding (e.g. bytes or JSON string).

Example fix

// before
Field.of("ts", FieldType.DATETIME) // no case in the Avro converter
// after
Field.of("ts", FieldType.INT64) // encode as epoch millis, or upgrade Beam for a DATETIME mapping

static final Set<TypeName> AVRO_SUPPORTED = Set.of(TypeName.BYTE, TypeName.INT16, TypeName.INT32, TypeName.INT64, TypeName.FLOAT, TypeName.DOUBLE, TypeName.BOOLEAN, TypeName.STRING, TypeName.BYTES, TypeName.DATETIME, TypeName.ARRAY, TypeName.ITERABLE, TypeName.MAP, TypeName.ROW);
static boolean isAvroSupported(FieldType ft) { return AVRO_SUPPORTED.contains(ft.getTypeName()); }

try {
  org.apache.avro.Schema s = AvroUtils.toAvroSchema(rowSchema);
} catch (IllegalArgumentException e) {
  if (e.getMessage() != null && e.getMessage().startsWith("Unexpected type ")) {
    throw new UnsupportedOperationException("Field type has no Avro mapping: " + e.getMessage(), e);
  }
  throw e;
}

When it happens

Trigger: Calling toAvroSchema/getFieldSchema with a FieldType whose TypeName is not covered by the switch (e.g. certain logical/container types or newly added Beam TypeNames not yet mapped to Avro).

Common situations: Newer Beam SDKs introducing TypeNames the Avro extension doesn't handle; passing DATETIME, BYTES-adjacent exotic types, or custom-type fields through Avro sink conversion.

Understand the failure class

Background: Type mismatch errors: IllegalArgumentException, TypeError and type guards across 150 open-source libraries — this error's family across 150 libraries.

Related errors

• Can't convert 'null' to FieldType
• Unhandled logical type ${identifier}
• Avro only supports maps with string keys
• Can't convert 'null' to non-nullable field
• Can't convert 'string' map keys to ${mapKeyType}

AI-assisted analysis of apache/beam@12126d8942 (2026-09-13). Data as JSON: /api/errors/be211870690340be. Report an issue: GitHub.