How update column updateDate , value is null

[khanhnam99]

How update column updateDate , value is null

use mysql 8
Incorrect date value: '' for column 'updateDate ' at row 1

$data = [
'updateDate ' => null
];
$db->update('TB_DISCOUNT', $data)

echo $db->getLastQuery();

// show query
// UPDATE TB_DISCOUNT updateDate = 'NULL'

how show query result like this:
UPDATE TB_DISCOUNT SET updateDate = NULL