Minor fix.

sql/database-create.sql

@@ -60,7 +60,7 @@ CREATE TABLE `active_checkups` (
 
 DROP TABLE IF EXISTS `apt_aggregates`;
 CREATE TABLE `apt_aggregates` (
-  `urn` varchar(128) default NULL,
+  `urn` varchar(128) NOT NULL default '',
   `name` varchar(32) NOT NULL default '',
   `nickname` varchar(32) NOT NULL default '',
   `abbreviation` varchar(16) NOT NULL default '',

sql/updates/4/458

@@ -10,7 +10,7 @@ sub DoUpdate($$$)
 
     if (!DBTableExists("apt_aggregates")) {
 	DBQueryFatal("CREATE TABLE `apt_aggregates` ( ".
-	     " `urn` varchar(128) default NULL, ".
+	     " `urn` varchar(128) NOT NULL default '', ".
 	     " `name` varchar(32) NOT NULL default '', ".
 	     " `nickname` varchar(32) NOT NULL default '', ".
 	     " `abbreviation` varchar(16) NOT NULL default '', ".