apache/flink · error · IllegalArgumentException

Missing type for included field

Error message

Missing type for included field {}.

What it means

Thrown by GenericCsvInputFormat.setFieldsGeneric(boolean[] includedMask, Class<?>[] fieldTypes) when the includedMask marks more fields as included than there are types supplied. Each 'true' in the mask consumes one type from fieldTypes; running out of types means a selected column has no declared type. The message names the offending field position i.

Solutions

1. Ensure fieldTypes.length equals the number of true entries in includedMask.
2. Build types from the mask in a single pass to keep them in sync.
3. Add a unit assertion counting true entries against the types array length.

Example fix

// before
boolean[] mask = {true, true, true};
Class<?>[] types = {Integer.class, String.class}; // only 2 types for 3 selected
format.setFieldsGeneric(mask, types);

// after
boolean[] mask = {true, true, true};
Class<?>[] types = {Integer.class, String.class, Double.class};
format.setFieldsGeneric(mask, types);

long selectedCount = Arrays.stream(includedMask).filter(b -> b).count();
if (selectedCount != fieldTypes.length) {
    throw new IllegalArgumentException(
        "included count (" + selectedCount + ") must equal fieldTypes.length (" + fieldTypes.length + ")");
}
format.setFieldsGeneric(includedMask, fieldTypes);

static boolean maskAndTypesAligned(boolean[] mask, Class<?>[] types) {
    long trues = mask == null ? -1 : Arrays.stream(mask).filter(b -> b).count();
    return trues == (types == null ? -1 : types.length);
}

When it happens

Trigger: includedMask has more true entries than fieldTypes.length; building the mask and types arrays from different sources that got out of sync; adding a column to the mask without adding its type.

Common situations: Schema evolution where a column was added to the selection but its type was forgotten; programmatic builders that construct mask and types separately; mismatched lengths after a refactor.

Related errors

• Field indices must not be smaller than zero.
• Field types must not be null.
• Type for included field
• Delimiter must not be null
• The field

AI-assisted analysis of apache/flink@2f3c205e92 (2026-08-14). Data as JSON: /api/errors/330efa6a2c61548d. Report an issue: GitHub.

Appendix: source

Thrown at flink-core/src/main/java/org/apache/flink/api/common/io/GenericCsvInputFormat.java:277

            }
        }

        this.fieldTypes = types.toArray(new Class<?>[types.size()]);
    }

    protected void setFieldsGeneric(boolean[] includedMask, Class<?>[] fieldTypes) {
        checkNotNull(includedMask);
        checkNotNull(fieldTypes);

        ArrayList<Class<?>> types = new ArrayList<Class<?>>();

        // check if types are valid for included fields
        int typeIndex = 0;
        for (int i = 0; i < includedMask.length; i++) {

            if (includedMask[i]) {
                if (typeIndex > fieldTypes.length - 1) {
                    throw new IllegalArgumentException(
                            "Missing type for included field " + i + ".");
                }
                Class<?> type = fieldTypes[typeIndex++];

                if (type == null) {
                    throw new IllegalArgumentException(
                            "Type for included field " + i + " should not be null.");
                } else {
                    // check if we support parsers for this type
                    if (FieldParser.getParserForType(type) == null) {
                        throw new IllegalArgumentException(
                                "The type '"
                                        + type.getName()
                                        + "' is not supported for the CSV input format.");
                    }
                    types.add(type);
                }
            }

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