What causes "isNull length is less than positionCount" in prestodb/presto?

Allocate valueIsNull with length >= arrayOffset + positionCount, mirroring values sizing.

prestodb/presto · error · IllegalArgumentException

isNull length is less than positionCount

Error message

isNull length is less than positionCount

What it means

ShortArrayBlock validates that the optional valueIsNull boolean array is at least arrayOffset + positionCount long whenever it is non-null. If isNull is shorter than the block's position range, null-lookups would read out of bounds, so the constructor throws IllegalArgumentException. The values and isNull arrays must have consistent capacity.

Source

Thrown at presto-common/src/main/java/com/facebook/presto/common/block/ShortArrayBlock.java:71

    ShortArrayBlock(int arrayOffset, int positionCount, boolean[] valueIsNull, short[] values)
    {
        if (arrayOffset < 0) {
            throw new IllegalArgumentException("arrayOffset is negative");
        }
        this.arrayOffset = arrayOffset;
        if (positionCount < 0) {
            throw new IllegalArgumentException("positionCount is negative");
        }
        this.positionCount = positionCount;

        if (values.length - arrayOffset < positionCount) {
            throw new IllegalArgumentException("values length is less than positionCount");
        }
        this.values = values;

        if (valueIsNull != null && valueIsNull.length - arrayOffset < positionCount) {
            throw new IllegalArgumentException("isNull length is less than positionCount");
        }
        this.valueIsNull = valueIsNull;

        retainedSizeInBytes = INSTANCE_SIZE + sizeOf(valueIsNull) + sizeOf(values);
    }

    @Override
    public long getSizeInBytes()
    {
        return SIZE_IN_BYTES_PER_POSITION * (long) positionCount;
    }

    @Override
    public OptionalInt fixedSizeInBytesPerPosition()
    {
        return OptionalInt.of(SIZE_IN_BYTES_PER_POSITION);
    }

View on GitHub (pinned to 55bb57d202)

Solutions

Allocate valueIsNull with length >= arrayOffset + positionCount, mirroring values sizing.
Pass null if no nulls are possible instead of an undersized mask.
Assert Arrays consistency: requireNonNull sizing helper before construction.

Example fix

// before
boolean[] isNull = new boolean[positionCount / 2];
new ShortArrayBlock(arrayOffset, positionCount, values, isNull);
// after
boolean[] isNull = new boolean[arrayOffset + positionCount];
new ShortArrayBlock(arrayOffset, positionCount, values, isNull);

Defensive patterns

Strategy: validation

Validate before calling

if (valueIsNull != null && valueIsNull.length - arrayOffset < positionCount) {
    throw new IllegalArgumentException("valueIsNull too small: need " + (arrayOffset + positionCount) + ", have " + valueIsNull.length);
}

Type guard

boolean nullMaskFits(int arrayOffset, int positionCount, boolean[] valueIsNull) {
    return valueIsNull == null || valueIsNull.length - arrayOffset >= positionCount;
}

Try / catch

try {
    block = new ShortArrayBlock(arrayOffset, positionCount, values, valueIsNull);
} catch (IllegalArgumentException e) {
    if (e.getMessage().contains("isNull length is less than positionCount")) {
        valueIsNull = valueIsNull == null ? null : Arrays.copyOf(valueIsNull, arrayOffset + positionCount);
        block = new ShortArrayBlock(arrayOffset, positionCount, values, valueIsNull);
    } else {
        throw e;
    }
}

Prevention

Keep values and valueIsNull sizing logic in a single helper so they can never diverge.
Pass null instead of an undersized mask when the block has no nulls.
After resizing values, always resize the null mask to match.

When it happens

Trigger: Constructing ShortArrayBlock with a non-null valueIsNull array where valueIsNull.length - arrayOffset < positionCount.

Common situations: Allocating the null mask from a different length source than the values array (e.g. reusing a stale mask after resizing), copy/paste where only values were grown, corrupted input data.

Related errors

AI-assisted analysis of prestodb/presto@55bb57d202 (2026-09-04). Data as JSON: /api/errors/bbc04719013a91ff. Report an issue: GitHub.