apache/cassandra · error · MarshalException

null is not supported inside collections

Error message

null is not supported inside collections

What it means

filterSortAndValidateElements checks each serialized element buffer of a list before it is stored. Cassandra forbids null elements inside collections; a null ByteBuffer triggers MarshalException with this message.

Source

Thrown at src/java/org/apache/cassandra/db/marshal/ListType.java:286

    @Override
    public void forEach(ByteBuffer input, Consumer<ByteBuffer> action)
    {
        serializer.forEach(input, action);
    }

    @Override
    public ByteBuffer getMaskedValue()
    {
        return decompose(Collections.emptyList());
    }

    @Override
    public List<ByteBuffer> filterSortAndValidateElements(List<ByteBuffer> buffers)
    {
        for (ByteBuffer buffer: buffers)
        {
            if (buffer == null)
                throw new MarshalException("null is not supported inside collections");
            elements.validate(buffer);
        }
        return buffers;
    }

    @Override
    public List<byte[]> filterSortAndValidateElementsFromArrays(List<byte[]> buffers)
    {
        for (byte[] buffer: buffers)
        {
            if (buffer == null)
                throw new MarshalException("null is not supported inside collections");
            elements.validate(buffer, ByteArrayAccessor.instance);
        }
        return buffers;
    }

    @Override

View on GitHub (pinned to 88fd0f6a0e)

Solutions

1. Filter out null buffers before calling filterSortAndValidateElements.
2. Use empty/serialized defaults instead of null where a placeholder is needed.
3. Validate the collection contents at the application boundary before writing.

Example fix

// before
List<ByteBuffer> bufs = rows.stream().map(r -> r.buf).collect(toList()); // may contain null
type.filterSortAndValidateElements(bufs);
// after
List<ByteBuffer> bufs = rows.stream().map(r -> r.buf).filter(Objects::nonNull).collect(toList());
type.filterSortAndValidateElements(bufs);

for (ByteBuffer b : buffers) { if (b == null) throw new IllegalArgumentException("null element buffer in list"); }

List<ByteBuffer> nonNull(List<ByteBuffer> in) { return in.stream().filter(Objects::nonNull).collect(Collectors.toList()); }

try { return listType.filterSortAndValidateElements(buffers); } catch (MarshalException e) { throw new DataConstraintException("List contains null elements", e); }

When it happens

Trigger: Programmatic use of ListType (e.g. building collection values via the driver or internal APIs) passing a list of ByteBuffers that contains null; deserialization paths constructing lists with null entries.

Common situations: Custom serialization code that leaves slots null; interop layers mapping nullable language collections directly onto Cassandra lists; drivers or tools that don't pre-filter nulls.

Related errors

• Invalid null element in list
• null is not supported inside vectors
• Element at index %d is null (expected type %s); given %s
• Output file name must not be null or empty.
• Command can not be null or blank string.

AI-assisted analysis of apache/cassandra@88fd0f6a0e (2026-09-10). Data as JSON: /api/errors/22a7ce85ee384077. Report an issue: GitHub.