Trouble with custom select field

[Antivirus]

I've created an array for my dropdown select field (in AdminCP) based on unique fields in a table like so:

PHP Code:

$dbdmas = $db->query_read("SELECT DISTINCT dmaname_clean, rank FROM " . TABLE_PREFIX . "dma ORDER BY dmaname_clean");

$dmas[0] = 'None Selected';
while ($dma = $db->fetch_array($dbdmas))
{
     $dmas[$dma['rank']] = $dma['dmaname_clean'] . " (" . $dma['rank'] . ")";


} 


As you can see, I added the 'None Selected' to the beginning of the array, and it shows as first value in the select field, however my problem is that when I select the value of 'None Selected', and save it, it inserts the value of '0' into the database. I want it to enter a blank value or NULL instead.


My code in AdminCP which is using the select menu is as follows:

PHP Code:

print_select_row($vbphrase['task_filter_dma'], $dmas, $taskft_dmanamearray, 0, 10, 1); 


The field in the table allows NULL values. Anyone know what my problem is please?