apache/cassandra · error · InvalidRequestException

Invalid null value for element selection on <columnName>

Error message

Invalid null value for element selection on <columnName>

What it means

For collection element selection (e.g. col[key] on a map/list/set column), the bound key value must be non-null; bindAndGet returning null (null literal or null bound variable) is rejected. (An UNSET marker is separately rejected with a sibling message.)

Source

Thrown at src/java/org/apache/cassandra/cql3/selection/ElementsSelector.java:154

     * is selected.
     * @param type the type of the collection.
     * @param key the element within the value represented by {@code factory} that is selected.
     * @return the created factory.
     */
    public static Factory newElementFactory(String name, Selector.Factory factory, CollectionType<?> type, final Term key)
    {
        return new AbstractFactory(name, factory, type)
        {
            protected AbstractType<?> getReturnType()
            {
                return valueType(type);
            }

            public Selector newInstance(QueryOptions options) throws InvalidRequestException
            {
                ByteBuffer keyValue = key.bindAndGet(options);
                if (keyValue == null)
                    throw new InvalidRequestException("Invalid null value for element selection on " + factory.getColumnName());
                if (keyValue == ByteBufferUtil.UNSET_BYTE_BUFFER)
                    throw new InvalidRequestException("Invalid unset value for element selection on " + factory.getColumnName());
                return new ElementSelector(factory.newInstance(options), keyValue);
            }

            public boolean areAllFetchedColumnsKnown()
            {
                // If we known all the fetched columns, it means that we don't have to wait execution to create
                // the ColumnFilter (through addFetchedColumns below).
                // That's the case if either there is no particular subselection
                // to add, or if there is one but the selected key is terminal. In other words,
                // we known all the fetched columns if all the feched columns of the factory are known and either:
                //  1) the type is frozen (in which case there isn't subselection to do).
                //  2) the factory (the left-hand-side) isn't a simple column selection (here again, no
                //     subselection we can do).
                //  3) the element selected is terminal.
                return factory.areAllFetchedColumnsKnown()
                        && (!type.isMultiCell() || !factory.isSimpleSelectorFactory() || key.isTerminal());

View on GitHub (pinned to 88fd0f6a0e)

Solutions

  1. Bind a concrete non-null key value before executing the statement.
  2. Remove the element-selection term if the key is unknown and filter/read the whole collection instead.
  3. Validate parameters at the application layer so null keys never reach the query.

Example fix

// before
BoundStatement bs = ps.bind(); // mapKey left unbound/null
session.execute(bs.bind("SELECT m[?] FROM t WHERE pk = ?", mapKey, pk));
// after
if (mapKey == null) throw new IllegalArgumentException("map key required");
session.execute(ps.bind(mapKey, pk));
Defensive patterns

Strategy: validation

Validate before calling

if (mapKey == null)
    throw new IllegalArgumentException("element selection key must not be null");
if (mapKey == ByteBufferUtil.UNSET_BYTE_BUFFER)
    throw new IllegalArgumentException("element selection key must be set");

Try / catch

try { session.execute(stmt); }
catch (InvalidRequestException e) {
    if (e.getMessage().contains("Invalid null value for element selection")) { /* fix bound key, retry */ }
    else throw e;
}

Prevention

When it happens

Trigger: A SELECT ... FROM t WHERE / selection using m[?] or m[null] where the marker is bound to null in QueryOptions, i.e. a null or missing bound value for the element-selection key.

Common situations: Driver statements with unset/null parameters for the map key in element selection; also literal 'm[null]' expressions written by mistake.

Related errors

AI-assisted analysis of apache/cassandra@88fd0f6a0e (2026-09-10). Data as JSON: /api/errors/544bfa851aac1f2f. Report an issue: GitHub.