presto-cassandra/src/main/java/io/prestosql/plugin/cassandra/CassandraType.java/CassandraType/getColumnValueForPartitionKey
class CassandraType:    public static NullableValue getColumnValueForPartitionKey(Row row, int position, CassandraType cassandraType)
    {
        Type nativeType = cassandraType.getNativeType();
        if (row.isNull(position)) {
            return NullableValue.asNull(nativeType);
        }
        switch (cassandraType) {
            case ASCII:
            case TEXT:
            case VARCHAR:
                return NullableValue.of(nativeType, utf8Slice(row.getString(position)));
            case UUID:
            case TIMEUUID:
                return NullableValue.of(nativeType, utf8Slice(row.getUUID(position).toString()));
            default:
                return getColumnValue(row, position, cassandraType);
        }
    }