Users not syncing with list. Wrong in filter?

I’ve added a filter to sync only users that exists in a database table. It looks like this:

add_filter( 'mailchimp_sync_should_sync_user', function( $subscribe, $user ) 
{
   $brukerid = $user->ID;
   $klasse = $wpdb->get_row( "SELECT * FROM klasser WHERE wpuserid='$brukerid'" );
   if( null !== $klasse ) 
   {
      return true;
   } 
   else 
   {
      return false;
   }
   
});

But the list in Mailchimp is still empty. I’ve tried manual sync, and debug looks like this for each user:
09:25:23Updating #995 4trinn <[email protected]>
09:25:23Error: null

Does Error: null, mean that there is an error?

• This topic was modified 8 years, 9 months ago by johnohod.