apache/flink · error · IllegalArgumentException

Unsupported type information '%s' for field '%s'.

Error message

Unsupported type information '%s' for field '%s'.

What it means

Thrown by the legacy TypeInformation path of CsvRowSchemaConverter: while mapping a field's TypeInformation to a Jackson CsvSchema.ColumnType, the type is none of the recognized numbers/strings/booleans/object arrays/row arrays/byte arrays. It is an IllegalArgumentException at schema-construction time — the table (or DataStream type) contains a field CSV cannot represent, e.g. MAP, MULTISET, or a custom type.

Source

Thrown at flink-formats/flink-csv/src/main/java/org/apache/flink/formats/csv/CsvRowSchemaConverter.java:200

        } else if (BOOLEAN_TYPES.contains(info)) {
            return CsvSchema.ColumnType.BOOLEAN;
        } else if (info instanceof ObjectArrayTypeInfo) {
            validateNestedField(fieldName, ((ObjectArrayTypeInfo) info).getComponentInfo());
            return CsvSchema.ColumnType.ARRAY;
        } else if (info instanceof BasicArrayTypeInfo) {
            validateNestedField(fieldName, ((BasicArrayTypeInfo) info).getComponentInfo());
            return CsvSchema.ColumnType.ARRAY;
        } else if (info instanceof RowTypeInfo) {
            final TypeInformation<?>[] types = ((RowTypeInfo) info).getFieldTypes();
            for (TypeInformation<?> type : types) {
                validateNestedField(fieldName, type);
            }
            return CsvSchema.ColumnType.ARRAY;
        } else if (info instanceof PrimitiveArrayTypeInfo
                && ((PrimitiveArrayTypeInfo) info).getComponentType() == Types.BYTE) {
            return CsvSchema.ColumnType.STRING;
        } else {
            throw new IllegalArgumentException(
                    "Unsupported type information '"
                            + info.toString()
                            + "' for field '"
                            + fieldName
                            + "'.");
        }
    }

    /**
     * Convert {@link LogicalType} to {@link CsvSchema.ColumnType} based on Jackson's categories.
     */
    private static CsvSchema.ColumnType convertType(String fieldName, LogicalType type) {
        if (STRING_TYPE_ROOTS.contains(type.getTypeRoot())) {
            return CsvSchema.ColumnType.STRING;
        } else if (NUMBER_TYPE_ROOTS.contains(type.getTypeRoot())) {
            return CsvSchema.ColumnType.NUMBER;
        } else if (BOOLEAN_TYPE_ROOTS.contains(type.getTypeRoot())) {
            return CsvSchema.ColumnType.BOOLEAN;

View on GitHub (pinned to 2f3c205e92)

Solutions

1. Cast or project the offending field to a supported type before CSV conversion (e.g. serialize MAP to STRING).
2. Flatten nested maps/rows into top-level primitive columns.
3. If structured output is required, switch to a format that supports maps (json, avro).

Example fix

// before: mapField is MapTypeInfo<String,Integer> in the RowTypeInfo
// throws at schema conversion

// after: pre-convert to string
DataStream<Row> flat = rows.map(r -> { r.setField(2, String.valueOf(r.getField(2))); return r; });

// Before building a CsvSchema from a RowTypeInfo:
for (TypeInformation<?> f : rowTypeInfo.getFieldTypes()) {
    if (!isCsvSupported(f)) throw new IllegalArgumentException(
        "Field type not CSV-representable: " + f);
}
boolean isCsvSupported(TypeInformation<?> t) {
    return t instanceof NumericTypeInfo || t instanceof BasicTypeInfo
        || t instanceof PrimitiveArrayTypeInfo
        || (t instanceof BasicArrayTypeInfo && isCsvSupported(((BasicArrayTypeInfo<?,?>) t).getComponentInfo()))
        || t instanceof RowTypeInfo;
}

static boolean isCsvSimpleType(TypeInformation<?> info) {
    return NUMBER_TYPES.contains(info) || STRING_TYPES.contains(info)
        || BOOLEAN_TYPES.contains(info);
}

When it happens

Trigger: Building a CsvSchema from a RowTypeInfo that includes MapTypeInfo, MultisetTypeInfo, or arbitrary ObjectArrayTypeInfo of complex elements; PojoTypeInfo fields inside arrays at top level of the row.

Common situations: DataStream CSV sinks (CsvWriter via RowTypeInfo) on types richer than the CSV feature supports; migrating jobs from JSON/Arrow formats that do allow maps.

Related errors

• Unsupported type '%s' for field '%s'.
• Only simple types are supported in the second level nesting
• Field types must not be null.
• Missing type for included field {}.
• Type for included field {} should not be null.

AI-assisted analysis of apache/flink@2f3c205e92 (2026-08-14). Data as JSON: /api/errors/b13ba1c5a7b68fff. Report an issue: GitHub.