apache/flink · error · IllegalArgumentException

The record must not be null.

Error message

The record must not be null.

What it means

CharPrimitiveArraySerializer writes the array length then each char. serialize() rejects null because a null array has no length to emit and primitive-array type information is non-nullable by contract.

Source

Thrown at flink-core/src/main/java/org/apache/flink/api/common/typeutils/base/array/CharPrimitiveArraySerializer.java:70

        char[] copy = new char[from.length];
        System.arraycopy(from, 0, copy, 0, from.length);
        return copy;
    }

    @Override
    public char[] copy(char[] from, char[] reuse) {
        return copy(from);
    }

    @Override
    public int getLength() {
        return -1;
    }

    @Override
    public void serialize(char[] record, DataOutputView target) throws IOException {
        if (record == null) {
            throw new IllegalArgumentException("The record must not be null.");
        }

        final int len = record.length;
        target.writeInt(len);
        for (int i = 0; i < len; i++) {
            target.writeChar(record[i]);
        }
    }

    @Override
    public char[] deserialize(DataInputView source) throws IOException {
        final int len = source.readInt();
        char[] result = new char[len];

        for (int i = 0; i < len; i++) {
            result[i] = source.readChar();
        }

View on GitHub (pinned to 2f3c205e92)

Solutions

1. Initialize char[] fields to an empty array instead of null before the sink/state.
2. Filter out records with null arrays upstream.
3. If nullability is legitimate, switch to an object/nullable type (e.g., Character[] or a Row with null handling).
4. Add a null check in your mapper to default null arrays to empty.

Example fix

// before: out.chars may be null -> serializer.serialize(chars) throws
// after: data.map(r -> { if (r.chars == null) r.chars = new char[0]; return r; })

// Validate before serialize
char[] safe = record == null ? new char[0] : record;
serializer.serialize(safe, target);

try {
    serializer.serialize(record, target);
} catch (IllegalArgumentException e) {
    if (e.getMessage().equals("The record must not be null.")) {
        record = new char[0];
        serializer.serialize(record, target);
    } else throw e;
}

When it happens

Trigger: Calling serialize(null, target) on the char[] serializer — a field typed char[] that resolved to null at runtime.

Common situations: A char[] field that is null due to a null source value or uninitialized POJO; a UDF returning null where a char array is expected; a nullable SQL column mapped to a primitive char[].

Related errors

• The record must not be null.
• The record must not be null.
• The record must not be null.
• The record must not be null.
• The record must not be null.

AI-assisted analysis of apache/flink@2f3c205e92 (2026-08-14). Data as JSON: /api/errors/a7732c46f356a974. Report an issue: GitHub.