presto-main/src/main/java/io/prestosql/type/UnknownType.java/UnknownType/getObjectValue
class UnknownType:    @Override
    public Object getObjectValue(ConnectorSession session, Block block, int position)
    {
        // call is null in case position is out of bounds
        checkArgument(block.isNull(position), "Expected NULL value for UnknownType");
        return null;
    }