apache/seatunnel · error · MongodbConnectorException

ILLEGAL_ARGUMENT

ILLEGAL_ARGUMENT

Error message

fieldName is empty

What it means

Constructor validation of DocumentRowDataDeserializer: the fieldNames array must be non-null and contain at least one column, because the deserializer maps every BSON document onto a SeaTunnelRow with those field names. An empty or null array makes row mapping impossible, so construction fails fast.

Source

Thrown at seatunnel-connectors-v2/connector-mongodb/src/main/java/org/apache/seatunnel/connectors/seatunnel/mongodb/serde/DocumentRowDataDeserializer.java:45

import static org.apache.seatunnel.api.table.type.SqlType.STRING;
import static org.apache.seatunnel.common.exception.CommonErrorCodeDeprecated.ILLEGAL_ARGUMENT;
import static org.apache.seatunnel.common.exception.CommonErrorCodeDeprecated.UNSUPPORTED_OPERATION;

public class DocumentRowDataDeserializer implements DocumentDeserializer<SeaTunnelRow> {

    private final String[] fieldNames;

    private final SeaTunnelDataType<?>[] fieldTypes;

    private final BsonToRowDataConverters bsonConverters;

    private final boolean flatSyncString;

    public DocumentRowDataDeserializer(
            String[] fieldNames, SeaTunnelDataType<?> dataTypes, boolean flatSyncString) {
        if (fieldNames == null || fieldNames.length < 1) {
            throw new MongodbConnectorException(ILLEGAL_ARGUMENT, "fieldName is empty");
        }
        this.bsonConverters = new BsonToRowDataConverters();
        this.fieldNames = fieldNames;
        this.fieldTypes = ((SeaTunnelRowType) dataTypes).getFieldTypes();
        this.flatSyncString = flatSyncString;
    }

    @Override
    public SeaTunnelRow deserialize(BsonDocument bsonDocument) {
        if (flatSyncString) {
            if (fieldNames.length != 1 && fieldTypes[0].getSqlType() != STRING) {
                throw new MongodbConnectorException(
                        UNSUPPORTED_OPERATION,
                        "By utilizing flatSyncString, only one field attribute value can be set, and the field type must be a String. This operation will perform a string mapping on a single MongoDB data entry.");
            }
            SeaTunnelRow rowData = new SeaTunnelRow(fieldNames.length);
            rowData.setField(
                    0, bsonConverters.createConverter(fieldTypes[0]).convert(bsonDocument));

View on GitHub (pinned to cf67b549a7)

Solutions

1. Provide a non-empty field list in the connector schema config (e.g. define 'schema' fields in the MongoDB source options).
2. Verify the SeaTunnelRowType passed to the deserializer has at least one field.
3. Check any query/projection options that could yield an empty column set.
4. If fields are derived dynamically, add a fallback/default field set before constructing the deserializer.

Example fix

// before
new DocumentRowDataDeserializer(new String[0], rowType, false) // throws
// after
new DocumentRowDataDeserializer(new String[]{"_id", "name"}, rowType, false)

// validate before construction
if (fieldNames == null || fieldNames.length == 0) { throw new IllegalArgumentException("at least one field is required"); }

try { deserializer = new DocumentRowDataDeserializer(fieldNames, rowType, flatSyncString); } catch (MongodbConnectorException e) { if (e.getMessage().equals("fieldName is empty")) { fieldNames = defaultFieldNames(); deserializer = new DocumentRowDataDeserializer(fieldNames, rowType, flatSyncString); } else { throw e; } }

When it happens

Trigger: Instantiating DocumentRowDataDeserializer with fieldNames == null or fieldNames.length == 0 — typically from a source connector built with an empty catalog table / query projection that resolved to zero columns.

Common situations: MongoDB source config where the 'schema'/'fields' option parses to an empty list; programmatic use of the connector API with an unpopulated SeaTunnelRowType; a projection/collection filter that matched no fields.

Understand the failure class

Background: "must not be empty", "cannot be empty" — required-field validation errors across open-source libraries — this error's family across 41 libraries.

Related errors

• FILE_SPLIT_SIZE_ILLEGAL
• UNSUPPORTED_DATA_TYPE
• ILLEGAL_ARGUMENT
• UNSUPPORTED_OPERATION
• UNSUPPORTED_DATA_TYPE

AI-assisted analysis of apache/seatunnel@cf67b549a7 (2026-09-10). Data as JSON: /api/errors/a01650b2656964f6. Report an issue: GitHub.