Hi AlexG,

I tested with the table content containing null and with empty data and it works as expected in the download option too.

Here is an eg:

CREATE TABLE my_table_null_test1 (
id INT,
name STRING
);

INSERT INTO my_table_null_test1 (id, name) VALUES
(1, 'John Doe'),
(2, NULL),
(3, 'Jane Doe'),
(NULL, 'Anonymous')
(4, '');

If you do not want nulls, you may have to modify the query to use 

coalesce(NULL, '') or

nvl(NULL, '');

 Hope it helps. Thanks!