apache/seatunnel · error · IllegalArgumentException

field_delimiter must not be null

Error message

field_delimiter must not be null

What it means

PythonSourceConfig.validate() throws this IllegalArgumentException when field_delimiter is null. Because the output format is text, the delimiter used to join/parse fields is mandatory and must be explicitly configured.

Source

Thrown at seatunnel-connectors-v2/connector-python/src/main/java/org/apache/seatunnel/connectors/seatunnel/python/source/PythonSourceConfig.java:98

    /**
     * Phase 1 keeps the stdout contract intentionally narrow so the first implementation can stay
     * compatible with the existing text deserializer.
     */
    private void validate() {
        if (StringUtils.isBlank(pythonExecutable)) {
            throw new IllegalArgumentException("python.executable must not be blank");
        }
        if (StringUtils.isBlank(pythonScriptPath)) {
            throw new IllegalArgumentException("python.script.path must not be blank");
        }
        if (!SUPPORTED_FILE_FORMAT.equalsIgnoreCase(fileFormatType)) {
            throw new IllegalArgumentException(
                    "Unsupported file_format_type: "
                            + fileFormatType
                            + ". Phase 1 supports only text");
        }
        if (fieldDelimiter == null) {
            throw new IllegalArgumentException("field_delimiter must not be null");
        }
    }
}

View on GitHub (pinned to cf67b549a7)

Solutions

1. Add field_delimiter to the config, e.g. field_delimiter = ",".
2. Use an explicit delimiter character matching what the Python script reads/writes.
3. Verify the option key spelling against the connector's Option definitions.
4. Note the check is for null, not blank — an empty string may pass; still set a meaningful delimiter.

Example fix

// before
Python {
  # field_delimiter omitted
}
// after
Python {
  field_delimiter = ","
}

// Java: delimiter must be present
Object delim = configMap.get("field_delimiter");
if (delim == null) {
    throw new IllegalArgumentException("field_delimiter is required for the Python text source");
}

try { cfg = new PythonSourceConfig(configMap); } catch (IllegalArgumentException e) { LOG.error("Invalid python source config: {}", e.getMessage()); }

When it happens

Trigger: Omitting field_delimiter from the Python source config; the option resolves to null during validate() and fails immediately.

Common situations: Assuming a default delimiter is applied when the option is absent; copying a minimal config example without the delimiter line; option name typo causing null resolution.

Understand the failure class

Background: "is required", "must be set", "missing required field": configuration validation errors across open-source libraries — this error's family across 36 libraries.

Related errors

• python.executable must not be blank
• python.script.path must not be blank
• FILE_SPLIT_FAIL
• Unsupported file_format_type: <fileFormatType>. Phase 1 supp
• The SQL config must contain at least one source table

AI-assisted analysis of apache/seatunnel@cf67b549a7 (2026-09-10). Data as JSON: /api/errors/4734736d7cf852ff. Report an issue: GitHub.