apache/cassandra · error · MarshalException

null is not supported inside collections

Error message

null is not supported inside collections

What it means

SetType validates every element buffer supplied when constructing a set value. Cassandra sets cannot contain null elements, so if any buffer in the incoming list is null the type throws this MarshalException before sorting/validating elements. It protects the internal sorted-set representation from nulls.

Source

Thrown at src/java/org/apache/cassandra/db/marshal/SetType.java:283

    @Override
    public List<ByteBuffer> filterSortAndValidateElements(List<ByteBuffer> buffers)
    {
        return filterSortAndValidateElements(buffers, ByteBufferAccessor.instance, elements.comparatorSet.buffer);
    }

    @Override
    public List<byte[]> filterSortAndValidateElementsFromArrays(List<byte[]> buffers)
    {
        return filterSortAndValidateElements(buffers, ByteArrayAccessor.instance, elements.comparatorSet.array);
    }

    private <V> List<V> filterSortAndValidateElements(List<V> buffers, ValueAccessor<V> valueAccessor, Comparator<V> comparator)
    {
        SortedSet<V> sorted = new TreeSet<>(comparator);
        for (V buffer: buffers)
        {
            if (buffer == null)
                throw new MarshalException("null is not supported inside collections");
            elements.validate(buffer, valueAccessor);
            sorted.add(buffer);
        }
        return new ArrayList<>(sorted);
    }

    @Override
    protected int compareNextCell(Iterator<Cell<?>> cellIterator, Iterator<ByteBuffer> elementIter)
    {
        return getElementsType().compare(cellIterator.next().path().get(0), elementIter.next());
    }

    @Override
    public boolean contains(ComplexColumnData columnData, ByteBuffer value)
    {
        return columnData.getCell(CellPath.create(value)) != null;
    }
}

View on GitHub (pinned to 88fd0f6a0e)

Solutions

1. Filter null elements out of the collection before passing it to SetType (builder.add / decompose).
2. Decide the desired semantics: skip nulls, or reject the record upstream with a clearer application-level error.
3. Check any JSON/JSONB deserialization path that maps missing fields to null elements and drop them instead.

Example fix

// before
List<ByteBuffer> elements = jsonList.stream().map(this::toByteBuffer).collect(toList());
set.decompose(elements);
// after
List<ByteBuffer> elements = jsonList.stream().filter(Objects::nonNull).map(this::toByteBuffer).collect(toList());
set.decompose(elements);

List<ByteBuffer> safe = elements == null ? Collections.emptyList() : elements.stream().filter(Objects::nonNull).collect(Collectors.toList());

When it happens

Trigger: Calling SetType.decompose / builder (e.g. SetType.getInstance(...).decompose or ListBox builder) with a list of ByteBuffer elements that contains a null entry; binding a CQL literal or bound value for a set column where one element is null (e.g. SET c = {1, null, 3}).

Common situations: Application code deserializing data from another source that represents missing values as null and passing them straight into a set builder; drivers/JSON-to-CQL converters that do not filter nulls before building collection values.

Related errors

• Unexpected extraneous bytes after + getCollectionName() + va
• Null value read when not allowed
• Not enough bytes to read a list
• Unexpected extraneous bytes after list value
• The data cannot be deserialized as a list

AI-assisted analysis of apache/cassandra@88fd0f6a0e (2026-09-10). Data as JSON: /api/errors/29e1b4258fb47d64. Report an issue: GitHub.