apache/cassandra · error · MarshalException

null is not supported inside collections

Error message

null is not supported inside collections

What it means

MapType.filterSortAndValidateElements() validates serialized map element pairs: it walks the serialized buffer in key/value pairs and throws MarshalException if any key or value byte slice is null. Null elements are not representable or permitted inside Cassandra collections.

Source

Thrown at src/java/org/apache/cassandra/db/marshal/MapType.java:422

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

    private <T> List<T> filterSortAndValidateElements(List<T> buffers, ValueAccessor<T> valueAccessor, Comparator<T> comparator)
    {
        // We depend on Maps to be properly sorted by their keys, so use a sorted map implementation here.
        SortedMap<T, T> map = new TreeMap<>(comparator);
        Iterator<T> iter = buffers.iterator();
        while (iter.hasNext())
        {
            T keyBytes = iter.next();
            T valueBytes = iter.next();

            if (keyBytes == null || valueBytes == null)
                throw new MarshalException("null is not supported inside collections");

            getKeysType().validate(keyBytes, valueAccessor);
            getValuesType().validate(valueBytes, valueAccessor);

            map.put(keyBytes, valueBytes);
        }

        List<T> sortedBuffers = new ArrayList<>(map.size() << 1);
        for (Map.Entry<T, T> entry : map.entrySet())
        {
            sortedBuffers.add(entry.getKey());
            sortedBuffers.add(entry.getValue());
        }
        return sortedBuffers;
    }

    protected int compareNextCell(Iterator<Cell<?>> cellIterator, Iterator<ByteBuffer> elementIter)
    {

View on GitHub (pinned to 88fd0f6a0e)

Solutions

1. Ensure map values bound to collection columns contain no null keys or null values; filter them out client-side before binding.
2. Use a separate DELETE statement to remove entries rather than binding null values.
3. Catch MarshalException around statement binding/execution and sanitize the collection input.

Example fix

// before
map.put(1, null); // bound to map<int,text> column
// after
map.remove(1); // or provide a non-null value

for (Map.Entry<K,V> e : boundMap.entrySet()) {
    if (e.getKey() == null || e.getValue() == null)
        throw new IllegalArgumentException("collection bind values must not contain null keys/values");
}

try {
    statement.bind(map);
} catch (MarshalException e) {
    if (e.getMessage().contains("null is not supported inside collections")) {
        // sanitize map and rebind
    }
}

When it happens

Trigger: Calling filterSortAndValidateElements (or filterSortAndValidateElementsFromArrays) with serialized map data containing null key or value buffers — typically from bind values where a map entry's key or value is null.

Common situations: Prepared-statement binds with Java maps containing null keys/values; protocol-level collection serialization bugs; client drivers encoding nulls into collection payloads.

Related errors

• Map keys cannot be null
• Map values cannot be null
• Invalid null key in map
• Invalid null value in map
• Null value read when not allowed

AI-assisted analysis of apache/cassandra@88fd0f6a0e (2026-09-10). Data as JSON: /api/errors/0c044e2e7f4aac89. Report an issue: GitHub.