presto-cassandra/src/main/java/io/prestosql/plugin/cassandra/CassandraMetadata.java/CassandraMetadata/listSchemas
class CassandraMetadata:    private List<String> listSchemas(ConnectorSession session, Optional<String> schemaName)
    {
        return schemaName.map(ImmutableList::of)
                .orElseGet(() -> (ImmutableList<String>) listSchemaNames(session));
    }