apache/cassandra · error · IllegalArgumentException

Value of type

Error message

Value of type 

What it means

ClusterMetadataTransformer.with(key, value) type-checks the value against the ExtensionKey's declared valueType. If obj is not an instance of key.valueType, an IllegalArgumentException naming the actual and expected types is thrown.

Source

Thrown at src/java/org/apache/cassandra/tcm/ClusterMetadata.java:940

                consensusMigrationState = new ConsensusMigrationState(Epoch.EMPTY, newTableMigrationStates);
            }
            return this;
        }

        public Transformer with(ConsensusMigrationState consensusMigrationState)
        {
            this.consensusMigrationState = consensusMigrationState;
            return this;
        }

        public Transformer with(ExtensionKey<?, ?> key, ExtensionValue<?> obj)
        {
            if (MetadataKeys.CORE_METADATA.containsKey(key))
                throw new IllegalArgumentException("Core cluster metadata objects should be addressed directly, " +
                                                   "not using the associated MetadataKey");

            if (!key.valueType.isInstance(obj))
                throw new IllegalArgumentException("Value of type " + obj.getClass() +
                                                   " is incompatible with type for key " + key +
                                                   " (" + key.valueType + ")");

            extensions.put(key, obj);
            modifiedKeys.add(key);
            return this;
        }

        public Transformer withIfAbsent(ExtensionKey<?, ?> key, ExtensionValue<?> obj)
        {
            if (extensions.containsKey(key))
                return this;
            return with(key, obj);
        }

        public Transformer without(ExtensionKey<?, ?> key)
        {
            if (MetadataKeys.CORE_METADATA.containsKey(key))

View on GitHub (pinned to 88fd0f6a0e)

Solutions

1. Pass a value whose runtime class matches (is an instance of) key.valueType.
2. Use the correct ExtensionKey for the value type being stored.
3. Add a local assert/instanceof check before calling with().

Example fix

// before
transformer.with(MY_KEY, stringValue); // MY_KEY.valueType is Integer
// after
transformer.with(MY_KEY, 42); // or use the key matching stringValue's type

if (!key.valueType.isInstance(value))
    throw new IllegalArgumentException("Value " + value + " does not match key type " + key.valueType);

static <T> boolean matchesKeyType(ExtensionKey<T,?> key, Object value) {
    return key.valueType.isInstance(value);
}

try {
    transformer.with(key, obj);
} catch (IllegalArgumentException e) {
    logger.error("Extension value type mismatch: {}", e.getMessage());
}

When it happens

Trigger: Calling with(ExtensionKey, ExtensionValue) where !key.valueType.isInstance(obj) — e.g. putting an object of the wrong class under an extension key, or mixing up keys between two extension types.

Common situations: Generic code passing Object/erased values, two extension keys with similar names swapped, or a value class changed without updating the ExtensionKey's valueType after a version upgrade.

Understand the failure class

Background: Type mismatch errors: IllegalArgumentException, TypeError and type guards across 150 open-source libraries — this error's family across 150 libraries.

Related errors

• Core cluster metadata objects should be addressed directly,
• Unknown endpoint %s
• Can only initialize cluster identifier during epoch %d, but
• Failed to find first CMS node in directory
• Cluster Metadata Identifier mismatch. Node is attempting to

AI-assisted analysis of apache/cassandra@88fd0f6a0e (2026-09-10). Data as JSON: /api/errors/177ea03a2a921eef. Report an issue: GitHub.