[NTLDR]

Yes, custom ones are stored in the database, in the userfields table.

Untest but should work, in member.php replace:

PHP Code:

$profilefield[value]=$userinfo[$profilefieldname]; 


With:

PHP Code:

if ($userinfo[$profilefieldname]=='') {
    $profilefield[value]="N/A";
} else {
    $profilefield[value]=$userinfo[$profilefieldname];
}