apache/flink · error · NullKeyFieldException

Field %s is null, but expected to hold a key.

Error message

Field %s is null, but expected to hold a key.

What it means

Error "Field %s is null, but expected to hold a key." thrown in apache/flink.

Source

Thrown at flink-core/src/main/java/org/apache/flink/types/Record.java:351

            }
        }
        return true;
    }

    /**
     * Gets the fields at the given positions into an array. If at any position a field is null,
     * then this method throws a @link NullKeyFieldException. All fields that have been successfully
     * read until the failing read are correctly contained in the record. All other fields are not
     * set.
     *
     * @param positions The positions of the fields to get.
     * @param targets The values into which the content of the fields is put.
     * @throws NullKeyFieldException in case of a failing field read.
     */
    public void getFieldsIntoCheckingNull(int[] positions, Value[] targets) {
        for (int i = 0; i < positions.length; i++) {
            if (!getFieldInto(positions[i], targets[i])) {
                throw new NullKeyFieldException(i);
            }
        }
    }

    /**
     * Deserializes the given object from the binary string, starting at the given position. If the
     * deserialization asks for more that <code>limit - offset</code> bytes, than an exception is
     * thrown.
     *
     * @param <T> The generic type of the value to be deserialized.
     * @param target The object to deserialize the data into.
     * @param offset The offset in the binary string.
     * @param limit The limit in the binary string.
     */
    private <T extends Value> void deserialize(T target, int offset, int limit, int fieldNumber) {
        final InternalDeSerializer serializer = this.serializer;
        serializer.memory = this.binaryData;
        serializer.position = offset;

View on GitHub (pinned to 2f3c205e92)

Solutions

1. Address the cause reported by the error message: Field the reported value is null, but expected to hold a key.
2. Verify the inputs, configuration values, and classpath/dependency setup related to this operation, then retry.

Example fix

Correct the condition described ("Field the reported value is null, but expected to hold a key.") and rerun the job or command.

When it happens

Trigger: Triggered at runtime when the operation fails because: Field the reported value is null, but expected to hold a key.

Common situations: Commonly caused by misconfiguration, missing dependencies or files, unsupported types or operations, or invalid user input leading to: Field the reported value is null, but expected to hold a key.

AI-assisted analysis of apache/flink@2f3c205e92 (2026-08-14). Data as JSON: /api/errors/d858494235fde338. Report an issue: GitHub.